Updated: 2022/Sep/29
Please read Privacy Policy. It's for your privacy.
ZDB(8) System Manager's Manual ZDB(8)
NAME
zdb - Display zpool debugging and consistency information
SYNOPSIS
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]
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. 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.
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/
(pool name followed by a slash).
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 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.
If specified multiple times provides greater and greater
verbosity.
If object IDs are specified, display information about those
specific objects only.
-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).
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.
-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.
-l device
Display the vdev labels from the specified device. If the -u
option is also specified, also display the uberblocks on this
device.
-L 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.
-m 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.
-M 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
d Decompress the block
e Byte swap the block
g Dump gang block header
i Dump indirect block
r Dump raw uninterpreted block data
-s Report statistics on zdb's 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.
-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.
-P 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.
-v Enable verbosity. Specify multiple times for increased
verbosity.
-X 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.
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)
AUTHORS
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>.
NetBSD 10.99 July 26, 2014 NetBSD 10.99