Provided by: zfsutils-linux_0.6.5.6-0ubuntu30_amd64 
NAME
zdb - Display zpool debugging and consistency information
SYNOPSIS
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
vdev:offset:size[:flags]
zdb -S [-AP] [-e [-p path...]] [-U cache] 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 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.
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.
-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 /etc/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.
-V
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.
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
ENVIRONMENT VARIABLES
SPA_CONFIG_PATH
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.
SEE ALSO
zfs(8), zpool(8)
February 15, 2012 ZDB(8)