Updated: February 15, 2012
- ENVIRONMENT VARIABLES
- SEE ALSO
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zdb - Display zpool debugging and consistency information
zdb [-CumdibcsDvhLMXFPA] [-e [-p path...]] [-t txg]
[-U cache] [-I inflight I/Os]
[poolname [object ...]]
zdb [-divPA] [-e [-p path...]] [-U cache]
dataset [object ...]
zdb -m [-MLXFPA] [-t txg] [-e [-p path...]] [-U cache]
poolname [vdev [metaslab ...]]
zdb -R [-A] [-e [-p path...]] [-U cache] poolname
zdb -S [-AP] [-e [-p path...]] [-U cache] poolname
zdb -l [-uA] device
zdb -C [-A] [-U cache]
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 an 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.
Display statistics regarding the number, size (logical, physical and
allocated) and deduplication of blocks.
Verify the checksum of all metadata blocks while printing block statistics
If specified multiple times, verify the checksums of all blocks.
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
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.
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.
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.
Display pool history similar to zpool history, but include internal
changes, transaction, and dataset information.
Display information about intent log (ZIL) entries relating to each
dataset. If specified multiple times, display counts of each intent log
Display the vdev labels from the specified device. If the -u option is
also specified, also display the uberblocks on this device.
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.
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.
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,
Print block pointer
Decompress the block
Byte swap the block
Dump gang block header
Dump indirect block
Dump raw uninterpreted block data
Report statistics on zdb's I/O. Display operation counts, bandwidth,
and error counts of I/O to the pool from zdb.
Simulate the effects of deduplication, constructing a DDT and then display
that DDT as with -DD.
Display the current uberblock.
Do not abort should any assertion fail.
Enable panic recovery, certain errors which would otherwise be fatal are
demoted to warnings.
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.
Attempt to make an unreadable pool readable by trying progressively older
-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
Print numbers in an unscaled form more amenable to parsing, eg. 1000000 rather
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.
Use a cache file other than /etc/zfs/zpool.cache.
Enable verbosity. Specify multiple times for increased verbosity.
Attempt 'extreme' transaction rewind, that is attempt the same recovery as
-F but read transactions otherwise deemed too old.
Attempt a verbatim import. This mimics the behavior of the kernel when loading
a pool from a cachefile.
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'
# zdb -C 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
# 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
Override the default spa_config_path (/etc/zfs/zpool.cache) setting. If -U flag is specified it will override this environment variable settings once again.