display zpool debugging and consistency information
path ...]] [
inflight I/Os] [
[poolname [object ...]]
path ...]] [
-p path ...]]
-p path ...]]
-p path ...]]
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(1M) nor an
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
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
When operating on an imported and active pool it is possible,
though unlikely, that zdb may interpret inconsistent pool data and behave
- 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
- 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
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
- 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.
- Display the statistics independently for each deduplication table.
- Dump the contents of the deduplication tables describing duplicate
- Also dump the contents of the deduplication tables describing unique
- Decode and display block from an embedded block pointer specified by the
- Display pool history similar to
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
- Examine the checkpointed state of the pool. Note, the on disk format of
the pool is not reverted to the checkpointed state.
- Read the vdev labels and L2ARC header from the specified device.
-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
-l will return 1. Each unique configuration is
displayed only once.
- 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).
- 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).
-q option is also specified,
don't print the labels or the L2ARC header.
-u option is also specified,
also display the uberblocks on this device. Specify multiple times to
- 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.
- Display the offset, spacemap, free space of each metaslab, all the log
spacemaps and their obsolete entry statistics.
- Also display information about the on-disk free space histogram associated
with each metaslab.
- Display the maximum contiguous free space, the in-core free space
histogram, and the percentage of free space in each space map.
- Display every spacemap record.
- Display the offset, spacemap, and free space of each metaslab.
- Also display information about the maximum contiguous free space and the
percentage of free space in each space map.
- Display every spacemap record.
- 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.
- 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
- b offset
- 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 I/O. Display operation
counts, bandwidth, and error counts of I/O to the pool from
- Simulate the effects of deduplication, constructing a DDT and then display
that DDT as with
- 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.
-p path ...]
- Operate on an exported pool, not present in
-p flag specifies the path under which devices are
to be searched.
- 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.
- Attempt to make an unreadable pool readable by trying progressively older
- Dump the contents of the zfs_dbgmsg buffer before exiting
zdb. zfs_dbgmsg is a buffer used by ZFS to dump
advanced debug information.
- Limit the number of outstanding checksum I/Os to the specified value. The
default value is 200. This option affects the performance of the
- 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
- Print numbers in an unscaled form more amenable to parsing, eg. 1000000
rather than 1M.
- Specify the highest transaction to use when searching for uberblocks. See
for a means to see the available uberblocks and their associated
- Use a cache file other than
- Enable verbosity. Specify multiple times for increased verbosity.
- Attempt verbatim import. This mimics the behavior of the kernel when
loading a pool from a cachefile. Only usable with
- 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.
- Example 1 Display the configuration of imported pool
# zdb -C rpool
- Example 2 Display basic dataset information about
# 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
# 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