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ZDB(8) System Manager's Manual ZDB(8) NAME zdb -- display ZFS storage pool debugging and consistency information SYNOPSIS zdb [-AbcdDFGhikLMNPsTvXYy] [-e [-V] [-p path]]a| [-I inflight-I/O-ops] [-o var=value]a| [-t txg] [-U cache] [-x dumpdir] [-K key] [poolname[/dataset|objset-ID]] [object|range]a| zdb [-AdiPv] [-e [-V] [-p path]]a| [-U cache] [-K key] poolname[/dataset|objset-ID] [object|range]a| zdb -B [-e [-V] [-p path]]a| [-U cache] [-K key] poolname/objset-ID [backup-flags] zdb -C [-A] [-U cache] [poolname] zdb -E [-A] word0:word1:a|:word15 zdb -l [-Aqu] device zdb -m [-AFLPXY] [-e [-V] [-p path]]a| [-t txg] [-U cache] poolname [vdev [metaslab]]a| zdb --allocated-map [-mAFLPXY] [-e [-V] [-p path]]a| [-t txg] [-U cache] poolname [vdev [metaslab]]a| zdb -O [-K key] dataset path zdb -r [-K key] dataset path destination zdb -r -O [-K key] dataset object-id destination zdb -R [-A] [-e [-V] [-p path]]a| [-U cache] poolname vdev:offset:[lsize/]psize[:flags] zdb -S [-AP] [-e [-V] [-p path]]a| [-U cache] poolname DESCRIPTION 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. It is not a fsck(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 invoca- tions 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/". zdb is an "offline" tool; it accesses the block devices underneath the pools directly from userspace and does not care if the pool is imported or datasets are mounted (or even if the system understands ZFS at all). When operating on an imported and active pool it is possible, though unlikely, that zdb may interpret inconsistent pool data and behave erratically. OPTIONS Display options: --allocated-map Prints out a list of all the allocated regions in the pool. Pri- marily intended for use with the zhack metaslab leak subcommand. -b, --block-stats Display statistics regarding the number, size (logical, physical and allocated) and deduplication of blocks. --bin=(lsize|psize|asize) When used with -bb, sort blocks into all three bins according to the given size (instead of binning a block for each size sepa- rately). For instance, with --bin=lsize, a block with lsize of 16K and psize of 4K will be added to the 16K bin in all three columns. --class=(normal|special|dedup|other)[,]a| When used with -bb, only consider blocks from these allocation classes. -B, --backup Generate a backup stream, similar to zfs send, but for the numeric objset ID, and without opening the dataset. This can be useful in recovery scenarios if dataset metadata has become corrupted but the dataset itself is readable. The optional flags argument is a string of one or more of the letters e, L, c, and w, which corre- spond to the same flags in zfs-send(8). -c, --checksum Verify the checksum of all metadata blocks while printing block statistics (see -b). If specified multiple times, verify the checksums of all blocks. -C, --config 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 dis- play 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. -d, --datasets Display information about datasets. Specified once, displays basic dataset information: ID, create transaction, size, and object count. See -N for determining if poolname[/dataset|objset-ID] is to use the specified dataset|objset-ID as a string (dataset name) or a number (objset ID) when datasets have numeric names. If specified multiple times provides greater and greater verbosity. If object IDs or object ID ranges are specified, display informa- tion about those specific objects or ranges only. An object ID range is specified in terms of a colon-separated tuple of the form <start>:<end>[:<flags>]. The fields start and end are integer object identifiers that denote the upper and lower bounds of the range. An end value of -1 specifies a range with no upper bound. The flags field optionally specifies a set of flags, de- scribed below, that control which object types are dumped. By de- fault, all object types are dumped. A minus sign (-) negates the effect of the flag that follows it and has no effect unless pre- ceded by the A flag. For example, the range 0:-1:A-d will dump all object types except for directories. A Dump all objects (this is the default) d Dump ZFS directory objects f Dump ZFS plain file objects m Dump SPA space map objects z Dump ZAP objects - Negate the effect of next flag -D, --dedup-stats 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 x compress / copies). -DD Display a histogram of deduplication statistics, showing the allo- cated (physically present on disk) and referenced (logically referenced in the pool) block counts and sizes by reference count. -DDD Display the statistics independently for each deduplication table. -DDDD Dump the contents of the deduplication tables describing duplicate blocks. -DDDDD Also dump the contents of the deduplication tables describing unique blocks. -E, --embedded-block-pointer=word0:word1:a|:word15 Decode and display block from an embedded block pointer specified by the word arguments. -h, --history Display pool history similar to zpool history, but include internal changes, transaction, and dataset information. -i, --intent-logs Display information about intent log (ZIL) entries relating to each dataset. If specified multiple times, display counts of each in- tent log transaction type. -k, --checkpointed-state Examine the checkpointed state of the pool. Note, the on disk for- mat of the pool is not reverted to the checkpointed state. -l, --label=device Read the vdev labels and L2ARC header from the specified device. zdb -l will return 0 if valid label was found, 1 if error occurred, and 2 if no valid labels were found. The presence of L2ARC header is indicated by a specific sequence (L2ARC_DEV_HDR_MAGIC). If there is an accounting error in the size or the number of L2ARC log blocks zdb -l will return 1. Each unique configuration is dis- played only once. -ll device In addition display label space usage stats. If a valid L2ARC header was found also display the properties of log blocks used for restoring L2ARC contents (persistent L2ARC). -lll device Display every configuration, unique or not. If a valid L2ARC header was found also display the properties of log entries in log blocks used for restoring L2ARC contents (persistent L2ARC). If the -q option is also specified, don't print the labels or the L2ARC header. If the -u option is also specified, also display the uberblocks on this device. Specify multiple times to increase verbosity. -L, --disable-leak-tracking Disable leak detection and the loading of space maps. By default, zdb verifies that all non-free blocks are referenced, which can be very expensive. -m, --metaslabs Display the offset, spacemap, free space of each metaslab, all the log spacemaps and their obsolete entry statistics. -mm Also display information about the on-disk free space histogram as- sociated with each metaslab. -mmm Display the maximum contiguous free space, the in-core free space histogram, and the percentage of free space in each space map. -mmmm Display every spacemap record. -M, --metaslab-groups Display all "normal" vdev metaslab group information - per-vdev metaslab count, fragmentation, and free space histogram, as well as overall pool fragmentation and histogram. -MM "Special" vdevs are added to -M's normal output. Also display in- formation about the maximum contiguous free space and the percent- age of free space in each space map. -MMM Display every spacemap record. -N Same as -d but force zdb to interpret the [dataset|objset-ID] in [poolname[/dataset|objset-ID]] as a numeric objset ID. -O, --object-lookups=dataset path Look up the specified path inside of the dataset and display its metadata and indirect blocks. Specified path must be relative to the root of dataset. This option can be combined with -v for in- creasing verbosity. -r, --copy-object=dataset path destination Copy the specified path inside of the dataset to the specified des- tination. Specified path must be relative to the root of dataset. When used with -O, the path argument is interpreted as an object identifier, not a path. This option can be combined with -v for increasing verbosity. -R, --read-block=poolname vdev:offset:[lsize/]psize[: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 physical size, or logical size / physical size) of the block to read and, optionally, flags (a set of flags, described below). b offset Print block pointer at hex offset c Calculate and display checksums d Decompress the block. Set environment variable ZDB_NO_ZLE to skip zle when guessing. e Byte swap the block g Dump gang block header i Dump indirect block r Dump raw uninterpreted block data v Verbose output for guessing compression algorithm -s, --io-stats Report statistics on zdb I/O. Display operation counts, bandwidth, and error counts of I/O to the pool from zdb. -S, --simulate-dedup Simulate the effects of deduplication, constructing a DDT and then display that DDT as with -DD. -T, --brt-stats Display block reference table (BRT) statistics, including the size of uniques blocks cloned, the space saving as a result of cloning, and the saving ratio. -TT Display the per-vdev BRT statistics, including total references. -TTT Display histograms of per-vdev BRT refcounts. -TTTT Dump the contents of the block reference tables. -u, --uberblock Display the current uberblock. Other options: -A, --ignore-assertions Do not abort should any assertion fail. -AA Enable panic recovery, certain errors which would otherwise be fa- tal are demoted to warnings. -AAA Do not abort if asserts fail and also enable panic recovery. -e, --exported=[-p path]a| 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, --dump-blocks=dumpdir All blocks accessed will be copied to files in the specified direc- tory. 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, --automatic-rewind Attempt to make an unreadable pool readable by trying progressively older transactions. -G, --dump-debug-msg Dump the contents of the zfs_dbgmsg buffer before exiting zdb. zfs_dbgmsg is a buffer used by ZFS to dump advanced debug informa- tion. -I, --inflight=inflight-I/O-ops Limit the number of outstanding checksum I/O operations to the specified value. The default value is 200. This option affects the performance of the -c option. -K, --key=key Decryption key needed to access an encrypted dataset. This will cause zdb to attempt to unlock the dataset using the encryption root, key format and other encryption parameters on the given dataset. zdb can still inspect pool and dataset structures on en- crypted datasets without unlocking them, but will not be able to access file names and attributes and object contents. WARNING: The raw decryption key and any decrypted data will be in user memory while zdb is running. Other user programs may be able to extract it by inspecting zdb as it runs. Exercise extreme caution when us- ing this option in shared or uncontrolled environments. -o, --option=var=valuea| Set the given tunable to the provided value. -o, --option=vara| Show the value of the given tunable. -o, --option=show Show all tunables and their values. -o, --option=info=valuea| Show info about a tunable, including their name, type and descrip- tion. -o, --option=info Show info about all tunables. -P, --parseable Print numbers in an unscaled form more amenable to parsing, e.g. 1000000 rather than 1M. -t, --txg=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=cachefile Use a cache file other than /etc/zfs/zpool.cache. -v, --verbose Enable verbosity. Specify multiple times for increased verbosity. -V, --verbatim Attempt verbatim import. This mimics the behavior of the kernel when loading a pool from a cachefile. Only usable with -e. -X, --extreme-rewind Attempt "extreme" transaction rewind, that is attempt the same re- covery as -F but read transactions otherwise deemed too old. -Y, --all-reconstruction Attempt all possible combinations when reconstructing indirect split blocks. This flag disables the individual I/O deadman timer in order to allow as much time as required for the attempted recon- struction. -y, --livelist Perform validation for livelists that are being deleted. Scans through the livelist and metaslabs, checking for duplicate entries and compares the two, checking for potential double frees. If it encounters issues, warnings will be printed, but the command will not necessarily fail. 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. EXIT STATUS The zdb utility exits 0 on success, 1 if a fatal error occurs, 2 if invalid command line options were specified, or 3 if on-disk corruption was de- tected, but was not fatal. EXAMPLES Example 1: Display the configuration of imported pool rpool # zdb -C rpool MOS Configuration: version: 28 name: 'rpool' a| 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 a| 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 a| dedup = 1.11, compress = 1.80, copies = 1.00, dedup * compress / copies = 2.00 SEE ALSO zfs(8), zpool(8) FreeBSD ports 15.quarterly August 12, 2025 ZDB(8)
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | EXAMPLES | SEE ALSO
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