zdb —
display
ZFS storage pool debugging and consistency information
| zdb |
[-AbcdDFGhikLMNPsvXYy]
[-e
[-V]
[-p
path]…]
[-I
inflight I/Os]
[-o
var=value]…
[-t
txg]
[-U
cache]
[-x
dumpdir]
[poolname[/dataset
| objset ID]]
[object|range…] |
| zdb |
[-AdiPv]
[-e
[-V]
[-p
path]…]
[-U
cache]
poolname[/dataset
| objset ID]
[object|range…] |
| zdb |
-E
[-A]
word0:word1:…:word15
|
| zdb |
-m
[-AFLPXY]
[-e
[-V]
[-p
path]…]
[-t
txg]
[-U
cache]
poolname
[vdev
[metaslab]…] |
| zdb |
-r 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
|
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 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/”.
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:
- -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 imported.
- -d
- 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
- 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
word0:word1:…:word15
- Decode and display block from an embedded block pointer
specified by the word arguments.
- -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.
- -k
- Examine the checkpointed state of the pool. Note, the on
disk format of the pool is not reverted to the checkpointed state.
-
-l
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 detection 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, 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
- Display the offset, spacemap, and free space of each
metaslab.
- -MM
- 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
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
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
- Report statistics on zdb 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 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.
- -F
- Attempt to make an unreadable pool readable by trying
progressively older transactions.
- -G
- 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 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.
-
-o
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
- Print numbers in an unscaled form more amenable to parsing,
e.g. 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
/etc/zfs/zpool.cache.
- -v
- Enable verbosity. Specify multiple times for increased
verbosity.
- -V
- Attempt verbatim import. This mimics the behavior of the
kernel when loading a pool from a cachefile. Only usable with
-e.
- -X
- Attempt “extreme” transaction rewind, that is
attempt the same recovery as -F but read
transactions otherwise deemed too old.
- -Y
- 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
- 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.
-
Example 1: Display the
configuration of imported pool rpool
-
-
Example 2: Display basic
dataset information about rpool
-
-
Example 3: Display basic
information about object 0 in
rpool/export/home
-
-
Example 4: Display the
predicted effect of enabling deduplication on
rpool
-
zfs(8),
zpool(8)