Updated: 2021/Apr/14

ZDB(8)                      System Manager's Manual                     ZDB(8)

     zdb - Display zpool debugging and consistency information

     zdb [-CumdibcsDvhLMXFPA] [-e [-p path...]] [-t txg] [-U cache]
         [-I inflight I/Os] [-x dumpdir] poolname [object ...]
     zdb [-divPA] [-e [-p path...]] [-U cache] dataset [object ...]
     zdb -m [-MLXFPA] [-t txg] [-e [-p path...]] [-U cache] poolname
     zdb -R [-A] [-e [-p path...]] [-U cache] poolname poolname
     zdb -S [-AP] [-e [-p path...]] [-U cache] poolname poolname
     zdb -l [-uA] device
     zdb -C [-A] [-U cache]

     The zdb utility displays information about a ZFS pool useful for
     debugging and performs some amount of consistency checking.  It is a not
     a general purpose tool and options (and facilities) may change.  This is
     neither a fsck(8) nor a fsdb(8) utility.

     The output of this command in general reflects the on-disk structure of a
     ZFS pool, and is inherently unstable.  The precise output of most
     invocations is not documented, a knowledge of ZFS internals is assumed.

     If the dataset argument does not contain any / or @ characters, it is
     interpreted as a pool name.  The root dataset can be specified as pool/
     (pool name followed by a slash).

     When operating on an imported and active pool it is possible, though
     unlikely, that zdb may interpret inconsistent pool data and behave

     Display options:

     -b      Display statistics regarding the number, size (logical, physical
             and allocated) and deduplication of blocks.

     -c      Verify the checksum of all metadata blocks while printing block
             statistics (see -b).

             If specified multiple times, verify the checksums of all blocks.

     -C      Display information about the configuration. If specified with no
             other options, instead display information about the cache file
             (/etc/zfs/zpool.cache).  To specify the cache file to display,
             see -U

             If specified multiple times, and a pool name is also specified
             display both the cached configuration and the on-disk
             configuration.  If specified multiple times with -e also display
             the configuration that would be used were the pool to be

     -d      Display information about datasets. Specified once, displays
             basic dataset information: ID, create transaction, size, and
             object count.

             If specified multiple times provides greater and greater

             If object IDs are specified, display information about those
             specific objects only.

     -D      Display deduplication statistics, including the deduplication
             ratio (dedup), compression ratio (compress), inflation due to the
             zfs copies property (copies), and an overall effective ratio
             (dedup * compress / copies).

             If specified twice, display a histogram of deduplication
             statistics, showing the allocated (physically present on disk)
             and referenced (logically referenced in the pool) block counts
             and sizes by reference count.

             If specified a third time, display the statistics independently
             for each deduplication table.

             If specified a fourth time, dump the contents of the
             deduplication tables describing duplicate blocks.

             If specified a fifth time, also dump the contents of the
             deduplication tables describing unique blocks.

     -h      Display pool history similar to zpool history, but include
             internal changes, transaction, and dataset information.

     -i      Display information about intent log (ZIL) entries relating to
             each dataset.  If specified multiple times, display counts of
             each intent log transaction type.

     -l device
             Display the vdev labels from the specified device.  If the -u
             option is also specified, also display the uberblocks on this

     -L      Disable leak tracing and the loading of space maps.  By default,
             zdb verifies that all non-free blocks are referenced, which can
             be very expensive.

     -m      Display the offset, spacemap, and free space of each metaslab.
             When specified twice, also display information about the on-disk
             free space histogram associated with each metaslab. When
             specified three time, display the maximum contiguous free space,
             the in-core free space histogram, and the percentage of free
             space in each space map.  When specified four times display every
             spacemap record.

     -M      Display the offset, spacemap, and free space of each metaslab.
             When specified twice, also display information about the maximum
             contiguous free space and the percentage of free space in each
             space map.  When specified three times display every spacemap

     -R poolname vdev:offset:size[:flags]
             Read and display a block from the specified device. By default
             the block is displayed as a hex dump, but see the description of
             the -r flag, below.

             The block is specified in terms of a colon-separated tuple vdev
             (an integer vdev identifier) offset (the offset within the vdev)
             size (the size of the block to read) and, optionally, flags (a
             set of flags, described below).

             b offset
                     Print block pointer

             d       Decompress the block

             e       Byte swap the block

             g       Dump gang block header

             i       Dump indirect block

             r       Dump raw uninterpreted block data

     -s      Report statistics on zdb's I/O.  Display operation counts,
             bandwidth, and error counts of I/O to the pool from zdb.

     -S      Simulate the effects of deduplication, constructing a DDT and
             then display that DDT as with -DD.

     -u      Display the current uberblock.

     Other options:

     -A      Do not abort should any assertion fail.

     -AA     Enable panic recovery, certain errors which would otherwise be
             fatal are demoted to warnings.

     -AAA    Do not abort if asserts fail and also enable panic recovery.

     -e [-p path...]
             Operate on an exported pool, not present in /etc/zfs/zpool.cache.
             The -p flag specifies the path under which devices are to be

     -x dumpdir
             All blocks accessed will be copied to files in the specified
             directory.  The blocks will be placed in sparse files whose name
             is the same as that of the file or device read.  zdb can be then
             run on the generated files.  Note that the -bbc flags are
             sufficient to access (and thus copy) all metadata on the pool.

     -F      Attempt to make an unreadable pool readable by trying
             progressively older transactions.

     -I inflight I/Os
             Limit the number of outstanding checksum I/Os to the specified
             value.  The default value is 200. This option affects the
             performance of the -c option.

     -P      Print numbers in an unscaled form more amenable to parsing, eg.
             1000000 rather than 1M.

     -t transaction
             Specify the highest transaction to use when searching for
             uberblocks.  See also the -u and -l options for a means to see
             the available uberblocks and their associated transaction

     -U cachefile
             Use a cache file other than /boot/zfs/zpool.cache.

     -v      Enable verbosity.  Specify multiple times for increased

     -X      Attempt `extreme' transaction rewind, that is attempt the same
             recovery as -F but read transactions otherwise deemed too old.

     Specifying a display option more than once enables verbosity for only
     that option, with more occurrences enabling more verbosity.

     If no options are specified, all information about the named pool will be
     displayed at default verbosity.

     Example 1 Display the configuration of imported pool 'rpool'

         # zdb -C rpool

         MOS Configuration:
                 version: 28
                 name: 'rpool'

     Example 2 Display basic dataset information about 'rpool'

         # zdb -d rpool
         Dataset mos [META], ID 0, cr_txg 4, 26.9M, 1051 objects
         Dataset rpool/swap [ZVOL], ID 59, cr_txg 356, 486M, 2 objects

     Example 3 Display basic information about object 0 in 'rpool/export/home'

         # zdb -d rpool/export/home 0
         Dataset rpool/export/home [ZPL], ID 137, cr_txg 1546, 32K, 8 objects

             Object  lvl   iblk   dblk  dsize  lsize   %full  type
                  0    7    16K    16K  15.0K    16K   25.00  DMU dnode

     Example 4 Display the predicted effect of enabling deduplication on

         # zdb -S rpool
         Simulated DDT histogram:

         bucket             allocated                      referenced
         ______  ______________________________  ______________________________
         refcnt  blocks   LSIZE   PSIZE   DSIZE  blocks   LSIZE   PSIZE   DSIZE
         ------  ------   -----   -----   -----  ------   -----   -----   -----
              1    694K   27.1G   15.0G   15.0G    694K   27.1G   15.0G   15.0G
              2   35.0K   1.33G    699M    699M   74.7K   2.79G   1.45G   1.45G
         dedup = 1.11, compress = 1.80, copies = 1.00, dedup * compress / copies = 2.00

     zfs(8), zpool(8)

     This manual page is a mdoc(7) reimplementation of the illumos manual page
     zdb(1M), modified and customized for FreeBSD and licensed under the
     Common Development and Distribution License (CDDL).

     The mdoc(7) implementation of this manual page was initially written by
     Martin Matuska <mm@FreeBSD.org> and
     Marcelo Araujo <araujo@FreeBSD.org>.

NetBSD 9.99                      July 26, 2014                     NetBSD 9.99