diff --git a/README b/README
index af07ff5..ab79a42 100644
--- a/README
+++ b/README
@@ -14,11 +14,14 @@ Block device layout:
     - u16                   version_minor
     /* Offset 8: parameters */
     - u16                   flags
-    - u8                    algorithm (1=lz4, 2=zlib, ...) [1]
-    - u8                    compression (1..9) [1]
+    - u8                    compression
+                              hi nybble: algorithm (1=lz4, 2=zlib, ...) [1]
+                              lo nybble: level (1..9) [1]
     - u8                    pblk_shift (0..3) [3 = 4kb]
     - u8                    lblk_shift (1..10) [4 = 64kb (*)]
-    - u16                   pbat_len [1]
+    - u8                    lba_elem_pblk_bytes (2, 4, 6)
+    - u8                    pbat_shift [0]
+    - u8                    pad
     - u32                   nr_zones
     - u32                   lblk_per_zone
     - byte[40]              reserved
diff --git a/cbd/cbd.c b/cbd/cbd.c
index 72517f2..40c6ed3 100644
--- a/cbd/cbd.c
+++ b/cbd/cbd.c
@@ -131,7 +131,7 @@ usage(void)
                     "\n");
     fprintf(stderr, "Commands:\n"
                     "  format [opts] <device>          Create (format) a compressed device\n"
-                    "    -P      --pbat-len              Physical block allocation table length [1]\n"
+                    "    -P      --pbat-size             Physical block allocation table size [1]\n"
                     "    -S      --pysical-size          Physical size [device size]\n"
                     "    -c      --compress-factor       Compression factor [2.0]\n"
                     "    -l      --logical-blksize       Logical block size\n"
@@ -169,7 +169,7 @@ do_format(int argc, char** argv)
 {
     static const char short_opts[] = "P:S:c:l:p:s:z:Z:";
     static const struct option long_opts[] = {
-        { "pbat-len",         required_argument, NULL, 'P' },
+        { "pbat-size",        required_argument, NULL, 'P' },
         { "physical-size",    required_argument, NULL, 'S' },
         { "compress-factor",  required_argument, NULL, 'c' },
         { "logical-blksize",  required_argument, NULL, 'l' },
@@ -186,12 +186,13 @@ do_format(int argc, char** argv)
     uint64_t lsize = 0;
     uint pblksize = PAGE_SIZE;
     uint lblksize = 16 * PAGE_SIZE;
-    uint16_t pbatlen = 1;
+    uint pbatsize = 1;
     enum cbd_alg alg = CBD_ALG_LZ4;
     uint level = 1;
 
     uint8_t pshift;
     uint8_t lshift;
+    uint8_t pbatshift;
 
     const char* dev;
 
@@ -204,7 +205,7 @@ do_format(int argc, char** argv)
             if (optval < 1) {
                 error("Size \"%s\" is not a valid pbat len\n", optarg);
             }
-            pbatlen = optval;
+            pbatsize = optval;
             break;
         case 'S':
             if (!parse_numeric_arg(optarg, &optval)) {
@@ -277,12 +278,16 @@ do_format(int argc, char** argv)
     if (lshift < LBLK_SHIFT_MIN || lshift > LBLK_SHIFT_MAX) {
         error("Invalid logical block size %u\n", lblksize);
     }
+    pbatshift = get_shift(pbatsize, 1);
+    if (pbatshift < PBAT_SHIFT_MIN || pbatshift > PBAT_SHIFT_MAX) {
+        error("Invalid pbat len %u\n", pbatsize);
+    }
     if (argc - optind != 1) {
         usage();
     }
     dev = argv[optind++];
 
-    cbd_format(dev, pshift, lshift, pbatlen, alg, level, psize, lsize);
+    cbd_format(dev, alg, level, pshift, lshift, pbatshift, psize, lsize);
 
     return 0;
 }
diff --git a/dm-compress/compress.c b/dm-compress/compress.c
index 8e4b83c..f87ad4c 100644
--- a/dm-compress/compress.c
+++ b/dm-compress/compress.c
@@ -78,25 +78,23 @@ static int
 compress_read_header(struct compress* c)
 {
     int ret = 0;
-    struct page* pblkpage;
-    u8 *pblkbuf;
-    struct page* iopagev[1];
+    struct page* page;
+    u8 *buf;
     struct cbd_header header;
 
-    pblkpage = cbd_alloc_page();
-    if (!pblkpage) {
+    page = cbd_alloc_page();
+    if (!page) {
         return -ENOMEM;
     }
-    pblkbuf = page_address(pblkpage);
-    iopagev[0] = pblkpage;
+    buf = page_address(page);
 
-    ret = pblk_read_wait(&c->kparams, 0, 1, iopagev);
+    ret = pblk_read_wait(&c->kparams, 0, 1, page);
     if (ret) {
         printk(KERN_ERR "%s: failed to read header\n", __func__);
         goto out;
     }
     memset(&header, 0, sizeof(header));
-    cbd_header_get(pblkbuf, &header);
+    cbd_header_get(buf, &header);
 
     if (memcmp(header.magic, CBD_MAGIC, sizeof(header.magic)) != 0) {
         printk(KERN_ERR "%s: bad magic\n", __func__);
@@ -158,13 +156,23 @@ compress_read_header(struct compress* c)
         ret = -EINVAL;
         goto out;
     }
+    if (pbat_len(&header.params) * pblk_size(&header.params) > PAGE_SIZE) {
+        printk(KERN_ERR "%s: pbat size too large\n", __func__);
+        ret = -EINVAL;
+        goto out;
+    }
+    if (lba_len(&header.params) > pblk_size(&header.params)) {
+        printk(KERN_ERR "%s: lba elem size too large\n", __func__);
+        ret = -EINVAL;
+        goto out;
+    }
 
     printk(KERN_INFO "%s: parameters...\n", __func__);
     printk(KERN_INFO "  compression=0x%02x\n", (unsigned int)header.params.compression);
     printk(KERN_INFO "  pblk_shift=%hu\n", (unsigned short)header.params.pblk_shift);
     printk(KERN_INFO "  lblk_shift=%hu\n", (unsigned short)header.params.lblk_shift);
     printk(KERN_INFO "  lba_elem_pblk_bytes=%hu\n", (unsigned short)header.params.lba_elem_pblk_bytes);
-    printk(KERN_INFO "  pbat_len=%hu\n", (unsigned short)header.params.pbat_len);
+    printk(KERN_INFO "  pbat_shift=%hu\n", (unsigned short)header.params.pbat_shift);
     printk(KERN_INFO "  nr_zones=%u\n", (unsigned int)header.params.nr_zones);
     printk(KERN_INFO "  lblk_per_zone=%u\n", (unsigned int)header.params.lblk_per_zone);
     printk(KERN_INFO "%s: stats...\n", __func__);
@@ -175,7 +183,7 @@ compress_read_header(struct compress* c)
     memcpy(&c->kstats.stats, &header.stats, sizeof(header.stats));
 
 out:
-    cbd_free_page(pblkpage);
+    cbd_free_page(page);
     return ret;
 }
 
@@ -183,29 +191,27 @@ static int
 compress_write_header(struct compress* c)
 {
     int ret = 0;
-    struct page* pblkpage;
-    u8* pblkbuf;
+    struct page* page;
+    u8* buf;
     struct cbd_header header;
-    struct page* iopagev[1];
 
-    pblkpage = cbd_alloc_page();
-    if (!pblkpage) {
+    page = cbd_alloc_page();
+    if (!page) {
         return -ENOMEM;
     }
-    pblkbuf = page_address(pblkpage);
+    buf = page_address(page);
     memset(&header, 0, sizeof(header));
     memcpy(header.magic, CBD_MAGIC, sizeof(header.magic));
     header.version_major = CBD_VERSION_MAJOR;
     header.version_minor = CBD_VERSION_MINOR;
     memcpy(&header.params, &c->kparams.params, sizeof(header.params));
     memcpy(&header.stats, &c->kstats.stats, sizeof(header.stats));
-    cbd_header_put(pblkbuf, &header);
-    iopagev[0] = pblkpage;
-    ret = pblk_write_wait(&c->kparams, 0, 1, iopagev);
+    cbd_header_put(buf, &header);
+    ret = pblk_write_wait(&c->kparams, 0, 1, page);
     if (ret) {
         printk(KERN_ERR "%s: failed to write header\n", __func__);
     }
-    cbd_free_page(pblkpage);
+    cbd_free_page(page);
 
     return ret;
 }
diff --git a/dm-compress/lbatpblk.c b/dm-compress/lbatpblk.c
index 4868e7d..0122212 100644
--- a/dm-compress/lbatpblk.c
+++ b/dm-compress/lbatpblk.c
@@ -69,6 +69,9 @@ lbatpblk_ctr(struct lbatpblk* lp,
 static void
 lbatpblk_dtr(struct lbatpblk* lp)
 {
+    if (lp->page) {
+        lock_page(lp->page);
+    }
     lp->buf = NULL;
     cbd_free_page(lp->page);
     lp->page = NULL;
@@ -84,7 +87,6 @@ static int
 lbatpblk_flush(struct lbatpblk* lp)
 {
     int ret = 0;
-    struct page* iopagev[1];
 
     mutex_lock(&lp->lock);
     if (!PageDirty(lp->page)) {
@@ -94,8 +96,7 @@ lbatpblk_flush(struct lbatpblk* lp)
         ret = -EIO;
         goto unlock;
     }
-    iopagev[0] = lp->page;
-    pblk_write(lp->kparams, lp->pblk, 1, iopagev);
+    pblk_write(lp->kparams, lp->pblk, 1, lp->page);
     mutex_unlock(&lp->lock);
     mutex_lock(&lp->kstats->lock);
     ++lp->kstats->lbatpblk_w;
@@ -114,10 +115,9 @@ static int
 lbatpblk_read(struct lbatpblk* lp)
 {
     int ret = 0;
-    struct page* pagev[1];
 
-    pagev[0] = lp->page;
-    ret = pblk_read_wait(lp->kparams, lp->pblk, 1, pagev);
+    BUG_ON(lbatpblk_error(lp));
+    ret = pblk_read_wait(lp->kparams, lp->pblk, 1, lp->page);
     mutex_lock(&lp->kstats->lock);
     ++lp->kstats->lbatpblk_r;
     mutex_unlock(&lp->kstats->lock);
diff --git a/dm-compress/lbatview.c b/dm-compress/lbatview.c
index 30e6eb3..fc64cf7 100644
--- a/dm-compress/lbatview.c
+++ b/dm-compress/lbatview.c
@@ -272,13 +272,11 @@ lbatview_elem_off(struct lbatview* lv, u64 lblk)
 static void
 lbatview_rmem(struct lbatview* lv, u32 off, u32 len, void* buf)
 {
-    /* XXX: Convert below to a BUG_ON */
-    if (off + len > 2 * PAGE_SIZE) {
-        printk(KERN_ERR "%s: *** out of bounds\n", __func__);
-        return;
-    }
-    if (off < PAGE_SIZE && off + len > PAGE_SIZE) {
-        u32 len0 = PAGE_SIZE - off;
+    u32 pblk_len = pblk_size(&lv->kparams->params);
+
+    BUG_ON(off + len > 2 * pblk_len);
+    if (off < pblk_len && off + len > pblk_len) {
+        u32 len0 = pblk_len - off;
         u8* pagebuf0 = lbatpblk_get_buf(lv->pages[0], false);
         u8* pagebuf1 = lbatpblk_get_buf(lv->pages[1], false);
         memcpy(buf, pagebuf0 + off, len0);
@@ -287,8 +285,8 @@ lbatview_rmem(struct lbatview* lv, u32 off, u32 len, void* buf)
         lbatpblk_put_buf(lv->pages[0]);
     }
     else {
-        u32 bufidx = off / PAGE_SIZE;
-        u32 bufoff = off % PAGE_SIZE;
+        u32 bufidx = off / pblk_len;
+        u32 bufoff = off % pblk_len;
         u8* pagebuf = lbatpblk_get_buf(lv->pages[bufidx], false);
         memcpy(buf, pagebuf + bufoff, len);
         lbatpblk_put_buf(lv->pages[bufidx]);
@@ -298,13 +296,11 @@ lbatview_rmem(struct lbatview* lv, u32 off, u32 len, void* buf)
 static void
 lbatview_wmem(struct lbatview* lv, u32 off, u32 len, void* buf)
 {
-    /* XXX: Convert below to a BUG_ON */
-    if (off + len > 2 * PAGE_SIZE) {
-        printk(KERN_ERR "%s: *** out of bounds\n", __func__);
-        return;
-    }
-    if (off < PAGE_SIZE && off + len > PAGE_SIZE) {
-        u32 len0 = PAGE_SIZE - off;
+    u32 pblk_len = pblk_size(&lv->kparams->params);
+
+    BUG_ON(off + len > 2 * pblk_len);
+    if (off < pblk_len && off + len > pblk_len) {
+        u32 len0 = pblk_len - off;
         u8* pagebuf0 = lbatpblk_get_buf(lv->pages[0], true);
         u8* pagebuf1 = lbatpblk_get_buf(lv->pages[1], true);
         memcpy(pagebuf0 + off, buf, len0);
@@ -313,8 +309,8 @@ lbatview_wmem(struct lbatview* lv, u32 off, u32 len, void* buf)
         lbatpblk_put_buf(lv->pages[0]);
     }
     else {
-        u32 bufidx = off / PAGE_SIZE;
-        u32 bufoff = off % PAGE_SIZE;
+        u32 bufidx = off / pblk_len;
+        u32 bufoff = off % pblk_len;
         u8* pagebuf = lbatpblk_get_buf(lv->pages[bufidx], true);
         memcpy(pagebuf + bufoff, buf, len);
         lbatpblk_put_buf(lv->pages[bufidx]);
diff --git a/dm-compress/lbd.c b/dm-compress/lbd.c
index 8222d0f..d268a49 100644
--- a/dm-compress/lbd.c
+++ b/dm-compress/lbd.c
@@ -259,7 +259,7 @@ lbd_ctr(struct lbd* lbd,
         struct lbatviewcache* lvc,
         void* percpu)
 {
-    u32 nr_pages = lblk_per_pblk(&kparams->params);
+    u32 nr_pages = DIV_ROUND_UP(lblk_size(&kparams->params), PAGE_SIZE);
 
     memset(lbd, 0, sizeof(struct lbd));
     INIT_LIST_HEAD(&lbd->lru_list);
@@ -281,9 +281,14 @@ lbd_ctr(struct lbd* lbd,
     if (!cbd_alloc_pagev(lbd->pagev, nr_pages)) {
         return false;
     }
-    lbd->buf = vmap(lbd->pagev, nr_pages, VM_MAP, PAGE_KERNEL);
-    if (!lbd->buf) {
-        return false;
+    if (nr_pages == 1) {
+        lbd->buf = page_address(lbd->pagev[0]);
+    }
+    else {
+        lbd->buf = vmap(lbd->pagev, nr_pages, VM_MAP, PAGE_KERNEL);
+        if (!lbd->buf) {
+            return false;
+        }
     }
     lbd->c_len = 0;
 
@@ -293,17 +298,30 @@ lbd_ctr(struct lbd* lbd,
 static void
 lbd_dtr(struct lbd* lbd)
 {
-    u32 nr_pages = lblk_per_pblk(&lbd->kparams->params);
+    u32 nr_pages = DIV_ROUND_UP(lblk_size(&lbd->kparams->params), PAGE_SIZE);
+    u32 n;
+
+    if (lbd->pagev) {
+        for (n = 0; n < nr_pages; ++n) {
+            if  (lbd->pagev[n]) {
+                lock_page(lbd->pagev[n]);
+            }
+        }
+    }
 
     if (lbatviewcache_put(lbd->lvc, lbd->lv) != 0) {
         printk(KERN_ERR "%s: lbatviewcache_put failed\n", __func__);
     }
     lbd->c_len = 0;
-    vunmap(lbd->buf);
+    if (nr_pages != 1) {
+        vunmap(lbd->buf);
+    }
     lbd->buf = NULL;
-    cbd_free_pagev(lbd->pagev, nr_pages);
-    kfree(lbd->pagev);
-    lbd->pagev = NULL;
+    if (lbd->pagev) {
+        cbd_free_pagev(lbd->pagev, nr_pages);
+        kfree(lbd->pagev);
+        lbd->pagev = NULL;
+    }
     lbd->percpu = NULL;
     lbd->lv = NULL;
     lbd->lvc = NULL;
@@ -319,12 +337,15 @@ static int
 lbd_flush(struct lbd* lbd)
 {
     int ret = 0;
+    u32 nr_pages = DIV_ROUND_UP(lblk_size(&lbd->kparams->params), PAGE_SIZE);
+    u32 pblk_per_page = PAGE_SIZE / pblk_size(&lbd->kparams->params);
     int err;
+    u32 nr_pblk;
+    u32 pblk_idx;
+    u32 pg_idx;
+    u64 pblkv[PBLK_IOV_MAX];
+    u32 iov_len;
     u32 n;
-    u64 pblk;
-    u32 nr_pages = lblk_per_pblk(&lbd->kparams->params);
-    u32 count;
-    struct page* iopagev[1];
 
     mutex_lock(&lbd->lock);
     if (!PageDirty(lbd->pagev[0])) {
@@ -346,30 +367,30 @@ lbd_flush(struct lbd* lbd)
         if (c_blkrem) {
             memset(lbd->buf + lbd->c_len, 0, c_blkrem);
         }
-        count = DIV_ROUND_UP(lbd->c_len, pblk_size(&lbd->kparams->params));
+        nr_pblk = DIV_ROUND_UP(lbd->c_len, pblk_size(&lbd->kparams->params));
     }
     else {
         lbd->c_len = CBD_UNCOMPRESSED;
-        count = lblk_per_pblk(&lbd->kparams->params);
+        nr_pblk = lblk_per_pblk(&lbd->kparams->params);
     }
     ret = lbatview_elem_realloc(lbd->lv, lbd->lblk, lbd->c_len);
     if (ret) {
         lbd->kparams->params.flags |= CBD_FLAG_ERROR;
         goto unlock;
     }
-    for (n = 0; n < count; ++n) {
-        pblk = lbatview_elem_pblk(lbd->lv, lbd->lblk, n);
-        BUG_ON(pblk == PBLK_NONE);
-        iopagev[0] = lbd->pagev[n];
-        pblk_write(lbd->kparams, pblk, 1, iopagev);
+    for (pblk_idx = 0, pg_idx = 0; pblk_idx < nr_pblk; ++pg_idx) {
+        iov_len = min(nr_pblk - pblk_idx, pblk_per_page);
+        for (n = 0; n < iov_len; ++n) {
+            pblkv[n] = lbatview_elem_pblk(lbd->lv, lbd->lblk, pblk_idx++);
+        }
+        pblk_writev(lbd->kparams, pblkv, iov_len, lbd->pagev[pg_idx]);
+    }
+    while (pg_idx < nr_pages) {
+        unlock_page(lbd->pagev[pg_idx++]);
     }
     mutex_lock(&lbd->kstats->lock);
     ++lbd->kstats->lbd_w;
     mutex_unlock(&lbd->kstats->lock);
-    while (n < lblk_per_pblk(&lbd->kparams->params)) {
-        unlock_page(lbd->pagev[n]);
-        ++n;
-    }
     goto out;
 
 unlock:
@@ -392,39 +413,36 @@ static int
 lbd_read(struct lbd* lbd)
 {
     int ret = 0;
-    u32 count;
+    u32 pblk_per_page = PAGE_SIZE / pblk_size(&lbd->kparams->params);
+    u32 nr_pblk;
+    u32 pblk_idx;
+    u32 pg_idx;
+    u64 pblkv[PBLK_IOV_MAX];
+    u32 iov_len;
     u32 n;
-    u64 pblk;
-    struct page* iopagev[1];
 
-    /* XXX: can't happen because lbdcache will not use a page with an error */
-    if (PageError(lbd->pagev[0])) {
-        return -EIO;
-    }
+    BUG_ON(lbd_error(lbd));
     lbd->c_len = lbatview_elem_len(lbd->lv, lbd->lblk);
     if (lbd->c_len == 0) {
         memset(lbd->buf, 0, lblk_size(&lbd->kparams->params));
     }
     else {
-        count = (lbd->c_len == CBD_UNCOMPRESSED) ?
+        nr_pblk = (lbd->c_len == CBD_UNCOMPRESSED) ?
                     lblk_per_pblk(&lbd->kparams->params) :
                     DIV_ROUND_UP(lbd->c_len, pblk_size(&lbd->kparams->params));
-        for (n = 0; n < count; ++n) {
-            pblk = lbatview_elem_pblk(lbd->lv, lbd->lblk, n);
-            if (pblk == PBLK_NONE) {
-                ret = -EIO;
-                goto out;
+        for (pblk_idx = 0, pg_idx = 0; pblk_idx < nr_pblk; ++pg_idx) {
+            iov_len = min(nr_pblk - pblk_idx, pblk_per_page);
+            for (n = 0; n < iov_len; ++n) {
+                pblkv[n] = lbatview_elem_pblk(lbd->lv, lbd->lblk, pblk_idx++);
             }
-            iopagev[0] = lbd->pagev[n];
-            /* XXX: Issue non-blocking reads? */
-            ret = pblk_read_wait(lbd->kparams, pblk, 1, iopagev);
+            ret = pblk_readv_wait(lbd->kparams, pblkv, iov_len, lbd->pagev[pg_idx]);
             if (ret) {
                 goto out;
             }
         }
         if (lbd->c_len != CBD_UNCOMPRESSED) {
             if (!lblk_decompress(lbd)) {
-                printk(KERN_ERR "  decompress failed\n");
+                printk(KERN_ERR "%s: decompress failed\n", __func__);
                 ret = -EIO;
                 goto out;
             }
@@ -443,7 +461,7 @@ static int
 lbd_reset(struct lbd* lbd, u64 lblk)
 {
     int ret = 0;
-    u32 nr_pages = lblk_per_pblk(&lbd->kparams->params);
+    u32 nr_pages = DIV_ROUND_UP(lblk_size(&lbd->kparams->params), PAGE_SIZE);
     u32 n;
 
     if (lbd->lv) { printk(KERN_ERR "%s: lbatview leak\n", __func__); }
@@ -496,11 +514,7 @@ lbd_lblk(struct lbd* lbd)
 void
 lbd_data_read(struct lbd* lbd, u32 off, u32 len, u8* buf)
 {
-    /* XXX: convert to BUG_ON */
-    if (off + len > lblk_size(&lbd->kparams->params)) {
-        printk(KERN_ERR "%s: out of bounds\n", __func__);
-        return;
-    }
+    BUG_ON(off + len > lblk_size(&lbd->kparams->params));
     mutex_lock(&lbd->lock);
     memcpy(buf, lbd->buf + off, len);
     mutex_unlock(&lbd->lock);
@@ -509,11 +523,7 @@ lbd_data_read(struct lbd* lbd, u32 off, u32 len, u8* buf)
 void
 lbd_data_write(struct lbd* lbd, u32 off, u32 len, const u8* buf)
 {
-    /* XXX: convert to BUG_ON */
-    if (off + len > lblk_size(&lbd->kparams->params)) {
-        printk(KERN_ERR "%s: out of bounds\n", __func__);
-        return;
-    }
+    BUG_ON(off + len > lblk_size(&lbd->kparams->params));
     mutex_lock(&lbd->lock);
     memcpy(lbd->buf + off, buf, len);
     SetPageDirty(lbd->pagev[0]);
@@ -564,7 +574,7 @@ lbdcache_alloc_compress_state(void* percpu, const struct cbd_params* params, int
         return false;
     }
 #ifdef COMPRESS_HAVE_LZ4
-    workmem_len = LZ4_compressBound(lblk_size(params));
+    workmem_len = LZ4_MEM_COMPRESS;
     state->lz4_workmem = vzalloc(workmem_len);
     if (!state->lz4_workmem) {
         return false;
diff --git a/dm-compress/pbat.c b/dm-compress/pbat.c
index e68e3e8..6349f70 100644
--- a/dm-compress/pbat.c
+++ b/dm-compress/pbat.c
@@ -40,7 +40,7 @@ struct pbat {
     struct compress_stats*      kstats;
     bool                        full;
     u32                         last_alloc;
-    struct page**               pagev;
+    struct page*                page;
     u8*                         buf;
 };
 
@@ -49,8 +49,6 @@ pbat_ctr(struct pbat* pbat,
          struct compress_params* kparams,
          struct compress_stats* kstats)
 {
-    u32 nr_pages = pbat_len(&kparams->params);
-
     memset(pbat, 0, sizeof(struct pbat));
     INIT_LIST_HEAD(&pbat->list);
     pbat->zone = ZONE_NONE;
@@ -61,22 +59,11 @@ pbat_ctr(struct pbat* pbat,
     pbat->kstats = kstats;
     pbat->full = false;
     pbat->last_alloc = 0;
-    pbat->pagev = kzalloc(nr_pages * sizeof(struct page*), GFP_KERNEL);
-    if (!pbat->pagev) {
+    pbat->page = cbd_alloc_page();
+    if (!pbat->page) {
         return false;
     }
-    if (!cbd_alloc_pagev(pbat->pagev, nr_pages)) {
-        return false;
-    }
-    if (nr_pages == 1) {
-        pbat->buf = page_address(pbat->pagev[0]);
-    }
-    else {
-        pbat->buf = vmap(pbat->pagev, nr_pages, VM_MAP, PAGE_KERNEL);
-        if (!pbat->buf) {
-            return false;
-        }
-    }
+    pbat->buf = page_address(pbat->page);
 
     return true;
 }
@@ -84,37 +71,28 @@ pbat_ctr(struct pbat* pbat,
 static void
 pbat_dtr(struct pbat* pbat)
 {
-    u32 nr_pages = pbat_len(&pbat->kparams->params);
-    u32 n;
-
-    for (n = 0; n < nr_pages; ++n) {
-        lock_page(pbat->pagev[n]);
-    }
-    if (nr_pages != 1) {
-        vunmap(pbat->buf);
+    if (pbat->page) {
+        lock_page(pbat->page);
     }
     pbat->buf = NULL;
-    cbd_free_pagev(pbat->pagev, nr_pages);
-    kfree(pbat->pagev);
-    pbat->pagev = NULL;
+    cbd_free_page(pbat->page);
+    pbat->page = NULL;
 }
 
 static bool
 pbat_error(struct pbat* pbat)
 {
-    return PageError(pbat->pagev[0]);
+    return PageError(pbat->page);
 }
 
 static int
 pbat_flush(struct pbat* pbat)
 {
     int ret = 0;
-    u32 nr_pages = pbat_len(&pbat->kparams->params);
-    u32 n;
     u64 pblk;
 
     mutex_lock(&pbat->lock);
-    if (!PageDirty(pbat->pagev[0])) {
+    if (!PageDirty(pbat->page)) {
         goto unlock;
     }
     if (pbat_error(pbat)) {
@@ -122,7 +100,7 @@ pbat_flush(struct pbat* pbat)
         goto unlock;
     }
     pblk = pbat_off(&pbat->kparams->params, pbat->zone);
-    pblk_write(pbat->kparams, pblk, nr_pages, pbat->pagev);
+    pblk_write(pbat->kparams, pblk, pbat_len(&pbat->kparams->params), pbat->page);
     mutex_unlock(&pbat->lock);
     mutex_lock(&pbat->kstats->lock);
     ++pbat->kstats->pbat_w;
@@ -131,9 +109,7 @@ pbat_flush(struct pbat* pbat)
     return ret;
 
 unlock:
-    for (n = 0; n < nr_pages; ++n) {
-        unlock_page(pbat->pagev[n]);
-    }
+    unlock_page(pbat->page);
     mutex_unlock(&pbat->lock);
 
     return ret;
@@ -143,15 +119,11 @@ static int
 pbat_read(struct pbat* pbat)
 {
     int ret = 0;
-    u32 nr_pages = pbat_len(&pbat->kparams->params);
     u64 pblk;
 
-    /* XXX: can't happen because pbatcache will not use a page with an error */
-    if (PageError(pbat->pagev[0])) {
-        return -EIO;
-    }
+    BUG_ON(pbat_error(pbat));
     pblk = pbat_off(&pbat->kparams->params, pbat->zone);
-    ret = pblk_read_wait(pbat->kparams, pblk, nr_pages, pbat->pagev);
+    ret = pblk_read_wait(pbat->kparams, pblk, pbat_len(&pbat->kparams->params), pbat->page);
     mutex_lock(&pbat->kstats->lock);
     ++pbat->kstats->pbat_r;
     mutex_unlock(&pbat->kstats->lock);
@@ -163,12 +135,8 @@ static int
 pbat_reset(struct pbat* pbat, u32 zone)
 {
     int ret = 0;
-    u32 nr_pages = pbat_len(&pbat->kparams->params);
-    u32 n;
 
-    for (n = 0; n < nr_pages; ++n) {
-        lock_page(pbat->pagev[n]);
-    }
+    lock_page(pbat->page);
     if (pbat->zone != zone) {
         pbat->zone = zone;
         pbat->full = false;
@@ -177,9 +145,7 @@ pbat_reset(struct pbat* pbat, u32 zone)
     }
 
     if (ret) {
-        for (n = 0; n < nr_pages; ++n) {
-            unlock_page(pbat->pagev[n]);
-        }
+        unlock_page(pbat->page);
         pbat->zone = ZONE_NONE;
     }
 
@@ -213,7 +179,7 @@ pbat_alloc(struct pbat* pbat)
     }
     pbat->last_alloc = idx;
     pblk = idx + zone_data_off(&pbat->kparams->params, pbat->zone);
-    SetPageDirty(pbat->pagev[0]);
+    SetPageDirty(pbat->page);
 
 out:
     mutex_unlock(&pbat->lock);
@@ -239,7 +205,7 @@ pbat_free(struct pbat* pbat, u64 pblk)
     mutex_lock(&pbat->lock);
     cbd_bitmap_free(pbat->buf, idx);
     pbat->full = false;
-    SetPageDirty(pbat->pagev[0]);
+    SetPageDirty(pbat->page);
     mutex_unlock(&pbat->lock);
 
     return 0;
diff --git a/dm-compress/util.c b/dm-compress/util.c
index 10a0faf..160bfee 100644
--- a/dm-compress/util.c
+++ b/dm-compress/util.c
@@ -99,12 +99,12 @@ cbd_free_pagev(struct page** pagev, size_t len)
 
 static struct bio*
 pblk_io_prepare(struct block_device* bdev, unsigned int op,
-        u32 pblk_size, u64 pblk, u32 count, struct page** pagev)
+        u32 pblk_len, u64 pblk, u32 count, struct page* page, u32 page_off)
 {
     struct bio* bio;
-    u32 n;
 
-    bio = bio_alloc(GFP_KERNEL, count);
+    BUG_ON(page_off + pblk_len * count > PAGE_SIZE);
+    bio = bio_alloc(GFP_KERNEL, 1);
     if (!bio) {
         printk(KERN_ERR "%s: out of memory\n", __func__);
         return NULL;
@@ -112,11 +112,9 @@ pblk_io_prepare(struct block_device* bdev, unsigned int op,
     bio_set_dev(bio, bdev);
     bio->bi_opf = op;
 
-    bio->bi_iter.bi_sector = pblk * (pblk_size / SECTOR_SIZE);
-    for (n = 0; n < count; ++n) {
-        if (bio_add_page(bio, pagev[n], pblk_size, 0) != pblk_size) {
-            BUG();
-        }
+    bio->bi_iter.bi_sector = pblk * (pblk_len / SECTOR_SIZE);
+    if (bio_add_page(bio, page, pblk_len * count, page_off) == 0) {
+        BUG();
     }
 
     return bio;
@@ -124,13 +122,13 @@ pblk_io_prepare(struct block_device* bdev, unsigned int op,
 
 int
 pblk_read_wait(struct compress_params* kparams,
-        u64 pblk, u32 count, struct page** pagev)
+        u64 pblk, u32 count, struct page* page)
 {
     int ret;
     struct bio* bio;
 
     bio = pblk_io_prepare(kparams->dev, REQ_OP_READ,
-            pblk_size(&kparams->params), pblk, count, pagev);
+            pblk_size(&kparams->params), pblk, count, page, 0);
     if (!bio) {
         printk(KERN_ERR "%s: out of memory\n", __func__);
         return -ENOMEM;
@@ -144,15 +142,44 @@ pblk_read_wait(struct compress_params* kparams,
     return ret;
 }
 
+int
+pblk_readv_wait(struct compress_params* kparams,
+        u64* pblkv, u32 count, struct page* page)
+{
+    int ret = 0;
+    u32 pblk_len = pblk_size(&kparams->params);
+    u32 n;
+    u32 page_off;
+    struct bio* bio;
+
+    /* XXX: Issue no-blocking reads for parallelism? */
+    for (n = 0, page_off = 0; n < count; ++n, page_off += pblk_len) {
+        bio = pblk_io_prepare(kparams->dev, REQ_OP_READ,
+                pblk_len, pblkv[n], 1, page, page_off);
+        if (!bio) {
+            printk(KERN_ERR "%s: out of memory\n", __func__);
+            return -ENOMEM;
+        }
+        ret = submit_bio_wait(bio);
+        if (ret) {
+            printk(KERN_ERR "%s: submit_bio_wait failed: %d\n", __func__, ret);
+            return ret;
+        }
+        bio_put(bio);
+    }
+
+    return ret;
+}
+
 int
 pblk_write_wait(struct compress_params* kparams,
-        u64 pblk, u32 count, struct page** pagev)
+        u64 pblk, u32 count, struct page* page)
 {
     int ret;
     struct bio* bio;
 
     bio = pblk_io_prepare(kparams->dev, REQ_OP_WRITE,
-            pblk_size(&kparams->params), pblk, count, pagev);
+            pblk_size(&kparams->params), pblk, count, page, 0);
     if (!bio) {
         printk(KERN_ERR "%s: out of memory\n", __func__);
         return -ENOMEM;
@@ -171,45 +198,120 @@ void
 pblk_write_endio(struct bio* bio)
 {
     struct compress_params* kparams = bio->bi_private;
-    u32 n;
-    struct page* page;
+    struct page* page = bio->bi_io_vec[0].bv_page;
 
-    BUG_ON(!bio);
     if (bio->bi_status != BLK_STS_OK) {
+        printk(KERN_ERR "%s: I/O error\n", __func__);
         kparams->params.flags |= CBD_FLAG_ERROR;
-        for (n = 0; n < bio->bi_max_vecs; ++n) {
-            page = bio->bi_io_vec[n].bv_page;
-            SetPageError(page);
-        }
-    }
-    for (n = 0; n < bio->bi_max_vecs; ++n) {
-        page = bio->bi_io_vec[n].bv_page;
-        ClearPageDirty(page);
-        unlock_page(page);
+        SetPageError(page);
     }
+    ClearPageDirty(page);
+    unlock_page(page);
     bio_put(bio);
 }
 
 void
 pblk_write(struct compress_params* kparams,
-        u64 pblk, u32 count, struct page** pagev)
+        u64 pblk, u32 count, struct page* page)
 {
     struct bio* bio;
-    u32 n;
 
     bio = pblk_io_prepare(kparams->dev, REQ_OP_WRITE,
-            pblk_size(&kparams->params), pblk, count, pagev);
+            pblk_size(&kparams->params), pblk, count, page, 0);
     if (!bio) {
         printk(KERN_ERR "%s: out of memory\n", __func__);
         kparams->params.flags |= CBD_FLAG_ERROR;
-        for (n = 0; n < count; ++n) {
-            SetPageError(pagev[n]);
-            unlock_page(pagev[n]);
-        }
+        SetPageError(page);
+        unlock_page(page);
         return;
     }
     bio->bi_end_io = pblk_write_endio;
     bio->bi_private = kparams;
-
     submit_bio(bio);
 }
+
+struct pblk_iov
+{
+    struct compress_params*     kparams;
+    atomic_t                    remain;
+};
+
+void
+pblk_writev_endio(struct bio* bio)
+{
+    struct pblk_iov* iov = bio->bi_private;
+    struct compress_params* kparams = iov->kparams;
+    struct page* page = bio->bi_io_vec[0].bv_page;
+
+    if (bio->bi_status != BLK_STS_OK) {
+        printk(KERN_ERR "%s: I/O error\n", __func__);
+        kparams->params.flags |= CBD_FLAG_ERROR;
+        SetPageError(page);
+    }
+    if (atomic_dec_and_test(&iov->remain)) {
+        ClearPageDirty(page);
+        unlock_page(page);
+        kfree(iov);
+    }
+    bio_put(bio);
+}
+
+void
+pblk_writev(struct compress_params* kparams,
+        u64* pblkv, u32 count, struct page* page)
+{
+    u32 pblk_len = pblk_size(&kparams->params);
+    struct pblk_iov* iov;
+    u32 idx;
+    u32 page_off;
+    u32 nr_bio;
+    u64 pblk;
+    u32 iov_nr_pblk;
+    struct bio* bio;
+
+    BUG_ON(pblk_len * count > PAGE_SIZE);
+    iov = kmalloc(sizeof(struct pblk_iov), GFP_KERNEL);
+    if (!iov) {
+        printk(KERN_ERR "%s: out of memory\n", __func__);
+        goto err;
+    }
+    iov->kparams = kparams;
+    atomic_set(&iov->remain, count);
+    idx = 0;
+    page_off = 0;
+    nr_bio = 0;
+    while (idx < count) {
+        pblk = pblkv[idx];
+        iov_nr_pblk = 1;
+        ++idx;
+        while (idx < count && pblkv[idx] == pblk + iov_nr_pblk) {
+            ++iov_nr_pblk;
+            ++idx;
+        }
+        bio = pblk_io_prepare(kparams->dev, REQ_OP_WRITE,
+            pblk_len, pblk, iov_nr_pblk, page, page_off);
+        if (!bio) {
+            printk(KERN_ERR "%s: out of memory\n", __func__);
+            goto err_free;
+        }
+        ++nr_bio;
+        bio->bi_end_io = pblk_writev_endio;
+        bio->bi_private = iov;
+        submit_bio(bio);
+        page_off += pblk_len * iov_nr_pblk;
+    }
+    if (atomic_sub_and_test(count - nr_bio, &iov->remain)) {
+        ClearPageDirty(page);
+        unlock_page(page);
+        kfree(iov);
+    }
+
+    return;
+
+err_free:
+    kfree(iov);
+err:
+    kparams->params.flags |= CBD_FLAG_ERROR;
+    SetPageError(page);
+    unlock_page(page);
+}
diff --git a/include/cbdutil.h b/include/cbdutil.h
index 2af81f1..a3d4e53 100644
--- a/include/cbdutil.h
+++ b/include/cbdutil.h
@@ -41,6 +41,6 @@ void __attribute__((noreturn))
         error(const char* fmt, ...);
 int     verbose(uint level, const char* fmt, ...);
 
-bool    ask_user_bool(const char* fmt, ...);
+bool    ask_user_bool(tristate_t auto_response, const char* fmt, ...);
 
 #endif
diff --git a/include/libcbd.h b/include/libcbd.h
index 2b8c596..83f7f1c 100644
--- a/include/libcbd.h
+++ b/include/libcbd.h
@@ -66,9 +66,9 @@ typedef enum {
 } tristate_t;
 
 int  cbd_format(const char* dev,
-                uint8_t pshift, uint8_t lshift,
-                uint16_t pbatlen,
                 enum cbd_alg alg, uint level,
+                uint8_t pshift, uint8_t lshift,
+                uint8_t pbatshift,
                 uint64_t psize, uint64_t lsize);
 int  cbd_open(const char* dev,
               const char* name);
diff --git a/include/linux/dm-compress.h b/include/linux/dm-compress.h
index 4b35dbf..b1547d5 100644
--- a/include/linux/dm-compress.h
+++ b/include/linux/dm-compress.h
@@ -5,6 +5,8 @@
 #define PBLK_SHIFT_MAX          3
 #define LBLK_SHIFT_MIN          1
 #define LBLK_SHIFT_MAX          10
+#define PBAT_SHIFT_MIN          0
+#define PBAT_SHIFT_MAX          3
 
 #define ZONE_NONE               (u32)(~0)
 #define PBLK_NONE               (u64)(~0)
@@ -35,7 +37,8 @@ struct cbd_params {
     u8                  pblk_shift;
     u8                  lblk_shift;
     u8                  lba_elem_pblk_bytes;
-    u16                 pbat_len;
+    u8                  pbat_shift;
+    /* u8 pad */
     u32                 nr_zones;
     u32                 lblk_per_zone;
 };
@@ -253,7 +256,7 @@ lblk_size(const struct cbd_params* params)
 static inline u32
 pbat_len(const struct cbd_params* params)
 {
-    return params->pbat_len;
+    return (1 << params->pbat_shift);
 }
 
 static inline u32
@@ -356,7 +359,8 @@ cbd_header_get(const u8* buf, struct cbd_header* header)
     header->params.pblk_shift = get_byte(&p);
     header->params.lblk_shift = get_byte(&p);
     header->params.lba_elem_pblk_bytes = get_byte(&p);
-    header->params.pbat_len = get16_le(&p);
+    header->params.pbat_shift = get_byte(&p);
+    p += 1; /* pad */
     header->params.nr_zones = get32_le(&p);
     header->params.lblk_per_zone = get32_le(&p);
     p = buf + 64;
@@ -377,7 +381,8 @@ cbd_header_put(u8* buf, const struct cbd_header* header)
     put_byte(&p, header->params.pblk_shift);
     put_byte(&p, header->params.lblk_shift);
     put_byte(&p, header->params.lba_elem_pblk_bytes);
-    put16_le(&p, header->params.pbat_len);
+    put_byte(&p, header->params.pbat_shift);
+    put_byte(&p, 0); /* pad */
     put32_le(&p, header->params.nr_zones);
     put32_le(&p, header->params.lblk_per_zone);
     p = buf + 64;
@@ -577,12 +582,17 @@ bool   cbd_alloc_pagev(struct page** pagev, size_t len);
 void   cbd_free_pagev(struct page** pagev, size_t len);
 
 /* Core low-level I/O */
+#define PBLK_IOV_MAX (PAGE_SIZE / SECTOR_SIZE)
 int    pblk_read_wait(struct compress_params* kparams,
-        u64 pblk, u32 count, struct page** pagev);
+        u64 pblk, u32 count, struct page* page);
+int    pblk_readv_wait(struct compress_params* kparams,
+        u64* pblkv, u32 count, struct page* page);
 int    pblk_write_wait(struct compress_params* kparams,
-        u64 pblk, u32 count, struct page** pagev);
+        u64 pblk, u32 count, struct page* page);
 void   pblk_write(struct compress_params* kparams,
-        u64 pblk, u32 count, struct page** pagev);
+        u64 pblk, u32 count, struct page* page);
+void   pblk_writev(struct compress_params* kparams,
+        u64* pblkv, u32 count, struct page* page);
 
 struct pbat;
 u32    pbat_zone(struct pbat* pbat);
diff --git a/libcbd/check.c b/libcbd/check.c
index 0a607db..9e4d6a1 100644
--- a/libcbd/check.c
+++ b/libcbd/check.c
@@ -10,6 +10,7 @@ typedef off_t off64_t;
 struct check_state
 {
     int                 fd;
+    tristate_t          auto_response;
     bool                check_lblk_data;
     bool                clean;
     u64                 pblk_used;
@@ -17,7 +18,6 @@ struct check_state
     u8**                pbatv;
 
     u8*                 compress_buf;
-    u8*                 lz4_workmem;
     z_stream            zlib_dstream;
 };
 
@@ -206,7 +206,8 @@ check_lblk_data(struct check_state* state,
     ret = check_decompress(state, params, data, len);
     free(data);
     if (!ret) {
-        if (ask_user_bool("lblk %u: failed to decompress. Clear?", lblk)) {
+        if (ask_user_bool(state->auto_response,
+                "lblk %u: failed to decompress. Clear?", lblk)) {
             memset(lba, 0, lba_len(params));
             return true;
         }
@@ -241,7 +242,8 @@ check_lblk_alloc(struct check_state* state,
         verbose(2, "  lblk[%u]: len=%u\n", lblk, len);
     }
     if (len > lblk_size(params)) {
-        if (ask_user_bool("lblk %u: length %u out of bounds. Clear?", lblk, len)) {
+        if (ask_user_bool(state->auto_response,
+                "lblk %u: length %u out of bounds. Clear?", lblk, len)) {
             memset(lba, 0, lba_len(params));
             return true;
         }
@@ -255,7 +257,8 @@ check_lblk_alloc(struct check_state* state,
         pblk = lba_pblk_get(params, buf, n);
         if (pblk < CBD_HEADER_BLOCKS) {
             verbose(2, "    [%u] :E: Alloc in header: %lu\n", n, pblk);
-            if (ask_user_bool("lblk %u: alloc %u in header. Clear?", lblk, n)) {
+            if (ask_user_bool(state->auto_response,
+                    "lblk %u: alloc %u in header. Clear?", lblk, n)) {
                 memset(lba, 0, lba_len(params));
                 return true;
             }
@@ -265,7 +268,8 @@ check_lblk_alloc(struct check_state* state,
         pblk_zone = zone_for_pblk(params, pblk);
         if (pblk_zone == ZONE_NONE || pblk_zone >= params->nr_zones) {
             verbose(2, "    [%u] :E: Alloc beyond end: %lu\n", n, pblk);
-            if (ask_user_bool("lblk %u: alloc %u beyond end. Clear?", lblk, n)) {
+            if (ask_user_bool(state->auto_response,
+                    "lblk %u: alloc %u beyond end. Clear?", lblk, n)) {
                 memset(lba, 0, lba_len(params));
                 return true;
             }
@@ -274,7 +278,8 @@ check_lblk_alloc(struct check_state* state,
         }
         if (pblk < zone_data_off(params, pblk_zone)) {
             verbose(2, "    [%u] :E: Alloc in metadata: %lu\n", n, pblk);
-            if (ask_user_bool("lblk %u alloc in medatada. Clear?", lblk)) {
+            if (ask_user_bool(state->auto_response,
+                    "lblk %u alloc in medatada. Clear?", lblk)) {
                 memset(lba, 0, lba_len(params));
                 return true;
             }
@@ -285,7 +290,8 @@ check_lblk_alloc(struct check_state* state,
         verbose(3, "    [%u] pblk=%lu\n", n, (unsigned long)pblk);
         if (cbd_bitmap_isset(state->pbatv[pblk_zone], pblk_off)) {
             verbose(2, "    [%u] :E: Duplicate allocation for pblk %lu\n", n, (unsigned long)pblk);
-            if (ask_user_bool("lblk %u duplicate alloc for pblk %lu. Clear?", lblk, pblk)) {
+            if (ask_user_bool(state->auto_response,
+                    "lblk %u duplicate alloc for pblk %lu. Clear?", lblk, pblk)) {
                 memset(lba, 0, lba_len(params));
                 return true;
             }
@@ -294,6 +300,8 @@ check_lblk_alloc(struct check_state* state,
         }
         cbd_bitmap_set(state->pbatv[pblk_zone], pblk_off);
     }
+    ++state->lblk_used;
+    state->pblk_used += n_alloc;
 
     return false;
 }
@@ -316,7 +324,7 @@ check_lbat(struct check_state* state, const struct cbd_params* params)
                 (unsigned long)zone_off(params, zone),
                 (unsigned long)(zone_data_off(params, zone) - 1),
                 (unsigned long)zone_data_off(params, zone),
-                (unsigned long)zone_off(params, zone + 1));
+                (unsigned long)(zone_off(params, zone + 1) - 1));
         for (n = 0; n < params->lblk_per_zone; ++n) {
             u8* buf = lbat + n * lba_len(params);
             if (lba_len_get(params, buf) != 0) {
@@ -331,7 +339,6 @@ check_lbat(struct check_state* state, const struct cbd_params* params)
         for (n = 0; n < params->lblk_per_zone; ++n) {
             u64 lblk = zone * params->lblk_per_zone + n;
             u8* buf = lbat + n * lba_len(params);
-            u32 len;
             if (check_lblk_alloc(state, params, lblk, buf)) {
                 changed = true;
             }
@@ -340,11 +347,6 @@ check_lbat(struct check_state* state, const struct cbd_params* params)
                     changed = true;
                 }
             }
-            len = lba_len_get(params, buf);
-            if (len != 0) {
-                ++state->lblk_used;
-                state->pblk_used += DIV_ROUND_UP(len, pblk_size(params));
-            }
         }
         if (changed) {
             lbat_write(state->fd, params, zone, lbat);
@@ -364,7 +366,8 @@ check_pbat(struct check_state* state, const struct cbd_params* params)
         bool changed = false;
         pbat_read(state->fd, params, zone, pbat);
         if (memcmp(pbat, state->pbatv[zone], pblk_size(params) * pbat_len(params)) != 0) {
-            if (ask_user_bool("zone %u has incorrect pbat. Fix?", zone)) {
+            if (ask_user_bool(state->auto_response,
+                    "zone %u has incorrect pbat. Fix?", zone)) {
                 memcpy(pbat, state->pbatv[zone], pblk_size(params) * pbat_len(params));
                 changed = true;
             }
@@ -395,8 +398,6 @@ cbd_check(const char* dev,
     if (state.fd < 0) {
         error("Cannot open device\n");
     }
-    state.check_lblk_data = full_check;
-    state.clean = true;
 
     verbose(1, "Reading header\n");
     pblk_read(state.fd, SECTOR_SIZE, 0, 1, buf);
@@ -409,16 +410,26 @@ cbd_check(const char* dev,
         return 0;
     }
 
+    state.auto_response = auto_response;
+    state.check_lblk_data = full_check;
+    state.clean = true;
     state.pbatv = calloc(header.params.nr_zones, sizeof(u8*));
     for (n = 0; n < header.params.nr_zones; ++n) {
         state.pbatv[n] = calloc(pblk_size(&header.params), pbat_len(&header.params));
     }
+    if (full_check) {
+        state.compress_buf = malloc(lblk_size(&header.params));
+        memset(state.compress_buf, 0, lblk_size(&header.params));
+        memset(&state.zlib_dstream, 0, sizeof(z_stream));
+        inflateInit2(&state.zlib_dstream, MAX_WBITS);
+    }
 
     verbose(1, "Checking lbat\n");
     check_lbat(&state, &header.params);
     verbose(1, "Checking pbat\n");
     check_pbat(&state, &header.params);
 
+    free(state.compress_buf);
     for (n = 0; n < header.params.nr_zones; ++n) {
         free(state.pbatv[n]);
     }
diff --git a/libcbd/format.c b/libcbd/format.c
index 112d234..c09556a 100644
--- a/libcbd/format.c
+++ b/libcbd/format.c
@@ -27,9 +27,9 @@ pblk_write(int fd, u32 pblk_size, u64 pblk, u32 count, const u8* data)
 
 int
 cbd_format(const char* dev,
-           uint8_t pshift, uint8_t lshift,
-           uint16_t pbatlen,
            enum cbd_alg alg, uint level,
+           uint8_t pshift, uint8_t lshift,
+           uint8_t pbatshift,
            uint64_t psize, uint64_t lsize)
 {
     int devfd;
@@ -45,6 +45,12 @@ cbd_format(const char* dev,
         error("Cannot open device\n");
     }
 
+    if (alg <= CBD_ALG_NONE || alg >= CBD_ALG_MAX) {
+        error("Compression algorithm %d unknown\n", (int)alg);
+    }
+    if (level < 1 || level > 9) {
+        error("Compression level %u out of bounds\n", level);
+    }
     if (!pshift) {
         pshift = CBD_DEFAULT_PHYSICAL_BLOCK_SHIFT;
     }
@@ -61,14 +67,9 @@ cbd_format(const char* dev,
                 (uint)lshift, (uint)LBLK_SHIFT_MIN, (uint)LBLK_SHIFT_MAX);
     }
     lblk_size = pblk_size * (1 << lshift);
-    if (!pbatlen) {
-        pbatlen = 1;
-    }
-    if (alg <= CBD_ALG_NONE || alg >= CBD_ALG_MAX) {
-        error("Compression algorithm %d unknown\n", (int)alg);
-    }
-    if (level < 1 || level > 9) {
-        error("Compression level %u out of bounds\n", level);
+    if (pbatshift < PBAT_SHIFT_MIN || pbatshift > PBAT_SHIFT_MAX) {
+        error("Physical block allocation table shift %u is not in [%u,%u]\n",
+                (uint)pbatshift, (uint)PBAT_SHIFT_MIN, (uint)PBAT_SHIFT_MAX);
     }
     if (!psize) {
         off_t pos;
@@ -92,7 +93,7 @@ cbd_format(const char* dev,
     printf("%s: parameters...\n", __func__);
     printf("  pshift=%u\n", (unsigned int)pshift);
     printf("  lshift=%u\n", (unsigned int)lshift);
-    printf("  pbatlen=%hu\n", (unsigned short)pbatlen);
+    printf("  pbatshift=%u\n", (unsigned int)pbatshift);
     printf("  alg=%d\n", (int)alg);
     printf("  level=%u\n", level);
     printf("  psize=%lu\n", (unsigned long)psize);
@@ -110,7 +111,7 @@ cbd_format(const char* dev,
     header.params.lba_elem_pblk_bytes =
             ((psize / pblk_size) <= 0xffff ? 2 :
                     ((psize / pblk_size) <= 0xffffffff ? 4 : 6));
-    header.params.pbat_len = pbatlen;
+    header.params.pbat_shift = pbatshift;
     /* XXX: Initial estimate */
     header.params.lblk_per_zone = zone_data_len(&header.params) * (lsize / lblk_size) / (psize / pblk_size);
     printf("  initial estimate for lblk_per_zone: %lu\n", (unsigned long)header.params.lblk_per_zone);
@@ -121,7 +122,7 @@ cbd_format(const char* dev,
     printf("  pblk_shift=%hu\n", (unsigned short)header.params.pblk_shift);
     printf("  lblk_shift=%hu\n", (unsigned short)header.params.lblk_shift);
     printf("  lba_elem_pblk_bytes=%hu\n", (unsigned short)header.params.lba_elem_pblk_bytes);
-    printf("  pbat_len=%hu\n", (unsigned short)header.params.pbat_len);
+    printf("  pbat_shift=%hu\n", (unsigned short)header.params.pbat_shift);
     printf("  nr_zones=%lu\n", (unsigned long)header.params.nr_zones);
     printf("  lblk_per_zone=%lu\n", (unsigned long)header.params.lblk_per_zone);
 
diff --git a/libcbd/util.c b/libcbd/util.c
index 7427a4b..71e8167 100644
--- a/libcbd/util.c
+++ b/libcbd/util.c
@@ -29,18 +29,27 @@ verbose(uint level, const char* fmt, ...)
 }
 
 bool
-ask_user_bool(const char* fmt, ...)
+ask_user_bool(tristate_t auto_response, const char* fmt, ...)
 {
     va_list ap;
-    char* line = NULL;
-    size_t len = 0;
+    char prompt[256];
+    char* line;
+    size_t len;
     int ret;
     bool answer;
 
     va_start(ap, fmt);
+    vsnprintf(prompt, sizeof(prompt), fmt, ap);
+    va_end(ap);
 again:
-    vprintf(fmt, ap);
-    printf(" [y/n]? ");
+    printf("%s [y/n]? ", prompt);
+    if (auto_response != t_none) {
+        answer = (auto_response == t_true);
+        printf("%s\n", (answer ? "y" : "n"));
+        return answer;
+    }
+    line = NULL;
+    len = 0;
     getline(&line, &len, stdin);
     if (ret > 0) {
         switch (line[0]) {