Provided by: zfsutils-linux_2.2.2-0ubuntu9_amd64 
NAME
zdb — display ZFS storage pool debugging and consistency information
SYNOPSIS
zdb [-AbcdDFGhikLMNPsTvXYy] [-e [-V] [-p path]…] [-I inflight-I/O-ops] [-o var=value]…
[-t txg] [-U cache] [-x dumpdir] [-K key] [poolname[/dataset|objset-ID]] [object|range…]
zdb [-AdiPv] [-e [-V] [-p path]…] [-U cache] [-K key] poolname[/dataset|objset-ID]
[object|range…]
zdb -B [-e [-V] [-p path]…] [-U cache] [-K key] poolname/objset-ID [backup-flags]
zdb -C [-A] [-U cache] [poolname]
zdb -E [-A] word0:word1:…:word15
zdb -l [-Aqu] device
zdb -m [-AFLPXY] [-e [-V] [-p path]…] [-t txg] [-U cache] poolname [vdev [metaslab]…]
zdb -O [-K key] dataset path
zdb -r [-K key] dataset path destination
zdb -R [-A] [-e [-V] [-p path]…] [-U cache] poolname vdev:offset:[lsize/]psize[:flags]
zdb -S [-AP] [-e [-V] [-p path]…] [-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 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/".
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:
-b, --block-stats
Display statistics regarding the number, size (logical, physical and allocated) and
deduplication of blocks.
-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
correspond 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 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.
-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 information 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,
described below, that control which object types are dumped. By default, all object
types are dumped. A minus sign (-) negates the effect of the flag that follows it
and has no effect unless preceded 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 × compress / copies).
-DD 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.
-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:…: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 intent log transaction type.
-k, --checkpointed-state
Examine the checkpointed state of the pool. Note, the on disk format 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 displayed 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 associated 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.
-O, --object-lookups=dataset path
Also display information about the maximum contiguous free space and the percentage
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 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 increasing verbosity.
-r, --copy-object=dataset path destination
Copy the specified path inside of the dataset to the specified destination.
Specified path must be relative to the root of dataset. 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 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 fatal are demoted to
warnings.
-AAA Do not abort if asserts fail and also enable panic recovery.
-e, --exported=[-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, --dump-blocks=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, --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 information.
-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 encrypted 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 using this option in shared or uncontrolled environments.
-o, --option=var=value…
Set the given global libzpool variable to the provided value. The value must be an
unsigned 32-bit integer. Currently only little-endian systems are supported to
avoid accidentally setting the high 32 bits of 64-bit variables.
-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 recovery 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 reconstruction.
-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.
EXAMPLES
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
SEE ALSO
zfs(8), zpool(8)