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


zdbDisplay 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 vdev: offset: size[ : flags]

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.

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


Display options:
Display statistics regarding the number, size (logical, physical and allocated) and deduplication of blocks.
Verify the checksum of all metadata blocks while printing block statistics (see -b).

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

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 imported.

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 verbosity.

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

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.

Display pool history similar to zpool history, but include internal changes, transaction, and dataset information.
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 device.
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.
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.
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 record.
-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
Decompress the block
Byte swap the block
Dump gang block header
Dump indirect block
Dump raw uninterpreted block data
Report statistics on zdb's I/O. Display operation counts, bandwidth, and error counts of I/O to the pool from zdb.
Simulate the effects of deduplication, constructing a DDT and then display that DDT as with -DD.
Display the current uberblock.

Other options:

Do not abort should any assertion fail.
Enable panic recovery, certain errors which would otherwise be fatal are demoted to warnings.
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 searched.
-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.
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.
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 numbers.
-U cachefile
Use a cache file other than /boot/zfs/zpool.cache.
Enable verbosity. Specify multiple times for increased verbosity.
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 'rpool'

# 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>.

July 26, 2014 FreeBSD