man/man8/zdb.8

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.\" Copyright 2012, Richard Lowe.
.\" Copyright (c) 2012, 2019 by Delphix. All rights reserved.
.\" Copyright 2017 Nexenta Systems, Inc.
.\" Copyright (c) 2017 Lawrence Livermore National Security, LLC.
.\" Copyright (c) 2017 Intel Corporation.
.\"
.Dd August 12, 2025
.Dt ZDB 8
.Os
.
.Sh NAME
.Nm zdb
.Nd display ZFS storage pool debugging and consistency information
.Sh SYNOPSIS
.Nm
.Op Fl AbcdDFGhikLMNPsTvXYy
.Op Fl e Oo Fl V Oc Oo Fl p Ar path Oc Ns …
.Op Fl I Ar inflight-I/O-ops
.Oo Fl o Ar var Ns = Ns Ar value Oc Ns …
.Op Fl t Ar txg
.Op Fl U Ar cache
.Op Fl x Ar dumpdir
.Op Fl K Ar key
.Op Ar poolname Ns Op / Ns Ar dataset Ns | Ns Ar objset-ID
.Op Ar object Ns | Ns Ar range Ns …
.Nm
.Op Fl AdiPv
.Op Fl e Oo Fl V Oc Oo Fl p Ar path Oc Ns …
.Op Fl U Ar cache
.Op Fl K Ar key
.Ar poolname Ns Op Ar / Ns Ar dataset Ns | Ns Ar objset-ID
.Op Ar object Ns | Ns Ar range Ns …
.Nm
.Fl B
.Op Fl e Oo Fl V Oc Oo Fl p Ar path Oc Ns …
.Op Fl U Ar cache
.Op Fl K Ar key
.Ar poolname Ns Ar / Ns Ar objset-ID
.Op Ar backup-flags
.Nm
.Fl C
.Op Fl A
.Op Fl U Ar cache
.Op Ar poolname
.Nm
.Fl E
.Op Fl A
.Ar word0 : Ns Ar word1 Ns :…: Ns Ar word15
.Nm
.Fl l
.Op Fl Aqu
.Ar device
.Nm
.Fl m
.Op Fl AFLPXY
.Op Fl e Oo Fl V Oc Oo Fl p Ar path Oc Ns …
.Op Fl t Ar txg
.Op Fl U Ar cache
.Ar poolname Op Ar vdev Oo Ar metaslab Oc Ns …
.Nm
.Fl -allocated-map
.Op Fl mAFLPXY
.Op Fl e Oo Fl V Oc Oo Fl p Ar path Oc Ns …
.Op Fl t Ar txg
.Op Fl U Ar cache
.Ar poolname Op Ar vdev Oo Ar metaslab Oc Ns …
.Nm
.Fl O
.Op Fl K Ar key
.Ar dataset path
.Nm
.Fl r
.Op Fl K Ar key
.Ar dataset path destination
.Nm
.Fl R
.Op Fl A
.Op Fl e Oo Fl V Oc Oo Fl p Ar path Oc Ns …
.Op Fl U Ar cache
.Ar poolname vdev : Ns Ar offset : Ns Oo Ar lsize Ns / Oc Ns Ar psize Ns Op : Ns Ar flags
.Nm
.Fl S
.Op Fl AP
.Op Fl e Oo Fl V Oc Oo Fl p Ar path Oc Ns …
.Op Fl U Ar cache
.Ar poolname
.
.Sh DESCRIPTION
The
.Nm
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
.Pq and facilities
may change.
It is not a
.Xr fsck 8
utility.
.Pp
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.
.Pp
If the
.Ar dataset
argument does not contain any
.Qq Sy /
or
.Qq Sy @
characters, it is interpreted as a pool name.
The root dataset can be specified as
.Qq Ar pool Ns / .
.Pp
.Nm
is an
.Qq 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.
.
.Sh OPTIONS
Display options:
.Bl -tag -width Ds
.It Fl Sy -allocated-map
Prints out a list of all the allocated regions in the pool.
Primarily intended for use with the
.Nm zhack metaslab leak
subcommand.
.It Fl b , -block-stats
Display statistics regarding the number, size
.Pq logical, physical and allocated
and deduplication of blocks.
.It Fl B , -backup
Generate a backup stream, similar to
.Nm zfs Cm 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
.Ar flags
argument is a string of one or more of the letters
.Sy e ,
.Sy L ,
.Sy c ,
and
.Sy w ,
which correspond to the same flags in
.Xr zfs-send 8 .
.It Fl c , -checksum
Verify the checksum of all metadata blocks while printing block statistics
.Po see
.Fl b
.Pc .
.Pp
If specified multiple times, verify the checksums of all blocks.
.It Fl C , -config
Display information about the configuration.
If specified with no other options, instead display information about the cache
file
.Pq Pa /etc/zfs/zpool.cache .
To specify the cache file to display, see
.Fl U .
.Pp
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
.Fl e
also display the configuration that would be used were the pool to be imported.
.It Fl d , -datasets
Display information about datasets.
Specified once, displays basic dataset information: ID, create transaction,
size, and object count.
See
.Fl N
for determining if
.Ar poolname Ns Op / Ns Ar dataset Ns | Ns Ar objset-ID
is to use the specified
.Ar dataset Ns | Ns Ar objset-ID
as a string (dataset name) or a number (objset ID) when
datasets have numeric names.
.Pp
If specified multiple times provides greater and greater verbosity.
.Pp
If object IDs or object ID ranges are specified, display information about
those specific objects or ranges only.
.Pp
An object ID range is specified in terms of a colon-separated tuple of
the form
.Ao start Ac : Ns Ao end Ac Ns Op : Ns Ao flags Ac .
The fields
.Ar start
and
.Ar end
are integer object identifiers that denote the upper and lower bounds
of the range.
An
.Ar end
value of -1 specifies a range with no upper bound.
The
.Ar 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
.Pq -
negates the effect of the flag that follows it and has no effect unless
preceded by the
.Ar A
flag.
For example, the range 0:-1:A-d will dump all object types except for
directories.
.Pp
.Bl -tag -compact -width Ds
.It Sy A
Dump all objects (this is the default)
.It Sy d
Dump ZFS directory objects
.It Sy f
Dump ZFS plain file objects
.It Sy m
Dump SPA space map objects
.It Sy z
Dump ZAP objects
.It Sy -
Negate the effect of next flag
.El
.It Fl D , -dedup-stats
Display deduplication statistics, including the deduplication ratio
.Pq Sy dedup ,
compression ratio
.Pq Sy compress ,
inflation due to the zfs copies property
.Pq Sy copies ,
and an overall effective ratio
.Pq Sy dedup No \(mu Sy compress No / Sy copies .
.It Fl DD
Display a histogram of deduplication statistics, showing the allocated
.Pq physically present on disk
and referenced
.Pq logically referenced in the pool
block counts and sizes by reference count.
.It Fl DDD
Display the statistics independently for each deduplication table.
.It Fl DDDD
Dump the contents of the deduplication tables describing duplicate blocks.
.It Fl DDDDD
Also dump the contents of the deduplication tables describing unique blocks.
.It Fl E , -embedded-block-pointer Ns = Ns Ar word0 : Ns Ar word1 Ns :…: Ns Ar word15
Decode and display block from an embedded block pointer specified by the
.Ar word
arguments.
.It Fl h , -history
Display pool history similar to
.Nm zpool Cm history ,
but include internal changes, transaction, and dataset information.
.It Fl i , -intent-logs
Display information about intent log
.Pq ZIL
entries relating to each dataset.
If specified multiple times, display counts of each intent log transaction type.
.It Fl 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.
.It Fl l , -label Ns = Ns Ar device
Read the vdev labels and L2ARC header from the specified device.
.Nm Fl 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
.Nm Fl l
will return 1.
Each unique configuration is displayed only once.
.It Fl ll Ar 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).
.It Fl lll Ar 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).
.Pp
If the
.Fl q
option is also specified, don't print the labels or the L2ARC header.
.Pp
If the
.Fl u
option is also specified, also display the uberblocks on this device.
Specify multiple times to increase verbosity.
.It Fl L , -disable-leak-tracking
Disable leak detection and the loading of space maps.
By default,
.Nm
verifies that all non-free blocks are referenced, which can be very expensive.
.It Fl m , -metaslabs
Display the offset, spacemap, free space of each metaslab, all the log
spacemaps and their obsolete entry statistics.
.It Fl mm
Also display information about the on-disk free space histogram associated with
each metaslab.
.It Fl mmm
Display the maximum contiguous free space, the in-core free space histogram, and
the percentage of free space in each space map.
.It Fl mmmm
Display every spacemap record.
.It Fl 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.
.It Fl MM
"Special" vdevs are added to -M's normal output.
Also display information about the maximum contiguous free space and the
percentage of free space in each space map.
.It Fl MMM
Display every spacemap record.
.It Fl N
Same as
.Fl d
but force zdb to interpret the
.Op Ar dataset Ns | Ns Ar objset-ID
in
.Op Ar poolname Ns Op / Ns Ar dataset Ns | Ns Ar objset-ID
as a numeric objset ID.
.It Fl O , -object-lookups Ns = Ns Ar dataset path
Look up the specified
.Ar path
inside of the
.Ar dataset
and display its metadata and indirect blocks.
Specified
.Ar path
must be relative to the root of
.Ar dataset .
This option can be combined with
.Fl v
for increasing verbosity.
.It Fl r , -copy-object Ns = Ns Ar dataset path destination
Copy the specified
.Ar path
inside of the
.Ar dataset
to the specified destination.
Specified
.Ar path
must be relative to the root of
.Ar dataset .
This option can be combined with
.Fl v
for increasing verbosity.
.It Xo
.Fl R , -read-block Ns = Ns Ar poolname vdev : Ns Ar offset : Ns Oo Ar lsize Ns / Oc Ns Ar psize Ns Op : Ns Ar flags
.Xc
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
.Sy r
flag, below.
.Pp
The block is specified in terms of a colon-separated tuple
.Ar vdev
.Pq an integer vdev identifier
.Ar offset
.Pq the offset within the vdev
.Ar size
.Pq the physical size, or logical size / physical size
of the block to read and, optionally,
.Ar flags
.Pq a set of flags, described below .
.Pp
.Bl -tag -compact -width "b offset"
.It Sy b Ar offset
Print block pointer at hex offset
.It Sy c
Calculate and display checksums
.It Sy d
Decompress the block.
Set environment variable
.Nm ZDB_NO_ZLE
to skip zle when guessing.
.It Sy e
Byte swap the block
.It Sy g
Dump gang block header
.It Sy i
Dump indirect block
.It Sy r
Dump raw uninterpreted block data
.It Sy v
Verbose output for guessing compression algorithm
.El
.It Fl s , -io-stats
Report statistics on
.Nm zdb
I/O.
Display operation counts, bandwidth, and error counts of I/O to the pool from
.Nm .
.It Fl S , -simulate-dedup
Simulate the effects of deduplication, constructing a DDT and then display
that DDT as with
.Fl DD .
.It Fl 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.
.It Fl TT
Display the per-vdev BRT statistics, including total references.
.It Fl TTT
Display histograms of per-vdev BRT refcounts.
.It Fl TTTT
Dump the contents of the block reference tables.
.It Fl u , -uberblock
Display the current uberblock.
.El
.Pp
Other options:
.Bl -tag -width Ds
.It Fl A , -ignore-assertions
Do not abort should any assertion fail.
.It Fl AA
Enable panic recovery, certain errors which would otherwise be fatal are
demoted to warnings.
.It Fl AAA
Do not abort if asserts fail and also enable panic recovery.
.It Fl e , -exported Ns = Ns Oo Fl p Ar path Oc Ns …
Operate on an exported pool, not present in
.Pa /etc/zfs/zpool.cache .
The
.Fl p
flag specifies the path under which devices are to be searched.
.It Fl x , -dump-blocks Ns = Ns Ar 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.
.Nm
can be then run on the generated files.
Note that the
.Fl bbc
flags are sufficient to access
.Pq and thus copy
all metadata on the pool.
.It Fl F , -automatic-rewind
Attempt to make an unreadable pool readable by trying progressively older
transactions.
.It Fl G , -dump-debug-msg
Dump the contents of the zfs_dbgmsg buffer before exiting
.Nm .
zfs_dbgmsg is a buffer used by ZFS to dump advanced debug information.
.It Fl I , -inflight Ns = Ns Ar 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
.Fl c
option.
.It Fl K , -key Ns = Ns Ar key
Decryption key needed to access an encrypted dataset.
This will cause
.Nm
to attempt to unlock the dataset using the encryption root, key format and other
encryption parameters on the given dataset.
.Nm
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. \fBWARNING:\fP The raw decryption key and any decrypted data
will be in user memory while
.Nm
is running.
Other user programs may be able to extract it by inspecting
.Nm
as it runs.
Exercise extreme caution when using this option in shared or uncontrolled
environments.
.It Fl o , -option Ns = Ns Ar var Ns = Ns Ar value Ns …
Set the given tunable to the provided value.
.It Fl o , -option Ns = Ns Ar var Ns …
Show the value of the given tunable.
.It Fl o , -option Ns = Ns show
Show all tunables and their values.
.It Fl o , -option Ns = Ns info Ns = Ns Ar value Ns …
Show info about a tunable, including their name, type and description.
.It Fl o , -option Ns = Ns info
Show info about all tunables.
.It Fl P , -parseable
Print numbers in an unscaled form more amenable to parsing, e.g.\&
.Sy 1000000
rather than
.Sy 1M .
.It Fl t , -txg Ns = Ns Ar transaction
Specify the highest transaction to use when searching for uberblocks.
See also the
.Fl u
and
.Fl l
options for a means to see the available uberblocks and their associated
transaction numbers.
.It Fl U , -cachefile Ns = Ns Ar cachefile
Use a cache file other than
.Pa /etc/zfs/zpool.cache .
.It Fl v , -verbose
Enable verbosity.
Specify multiple times for increased verbosity.
.It Fl V , -verbatim
Attempt verbatim import.
This mimics the behavior of the kernel when loading a pool from a cachefile.
Only usable with
.Fl e .
.It Fl X , -extreme-rewind
Attempt
.Qq extreme
transaction rewind, that is attempt the same recovery as
.Fl F
but read transactions otherwise deemed too old.
.It Fl 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.
.It Fl 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.
.El
.Pp
Specifying a display option more than once enables verbosity for only that
option, with more occurrences enabling more verbosity.
.Pp
If no options are specified, all information about the named pool will be
displayed at default verbosity.
.
.Sh EXIT STATUS
The
.Nm
utility exits
.Sy 0
on success,
.Sy 1
if a fatal error occurs,
.Sy 2
if invalid command line options were specified, or
.Sy 3
if on-disk corruption was detected, but was not fatal.
.Sh EXAMPLES
.Ss Example 1 : No Display the configuration of imported pool Ar rpool
.Bd -literal
.No # Nm zdb Fl C Ar rpool
MOS Configuration:
        version: 28
        name: 'rpool'
 …
.Ed
.
.Ss Example 2 : No Display basic dataset information about Ar rpool
.Bd -literal
.No # Nm zdb Fl d Ar 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
 …
.Ed
.
.Ss Example 3 : No Display basic information about object 0 in Ar rpool/export/home
.Bd -literal
.No # Nm zdb Fl d Ar 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
.Ed
.
.Ss Example 4 : No Display the predicted effect of enabling deduplication on Ar rpool
.Bd -literal
.No # Nm zdb Fl S Ar 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
.Ed
.
.Sh SEE ALSO
.Xr zfs 8 ,
.Xr zpool 8