ZDB(8) Maintenance Commands and Procedures ZDB(8)

NAME

zdb - display zpool debugging and consistency information

SYNOPSIS

zdb [-AbcdDFGhikLMPsvX] [-e [-V] [-p path ...]] [-I inflight I/Os]
[-o var=value]... [-t txg] [-U cache] [-x dumpdir]
[poolname [object ...]]
zdb [-AdiPv] [-e [-V] [-p path ...]] [-U cache] dataset [object ...]
zdb -C [-A] [-U cache]
zdb -E [-A] word0:word1:...:word15
zdb -l [-Aqu] device
zdb -m [-AFLPX] [-e [-V] [-p path ...]] [-t txg] [-U cache]
poolname [vdev [metaslab ...]]
zdb -O dataset path
zdb -R [-A] [-e [-V] [-p path ...]] [-U cache]
poolname vdev:offset:size[:flags]
zdb -S [-AP] [-e [-V] [-p path ...]] [-U cache] poolname

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).

-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.

-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 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 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, 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.

-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.

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)

illumos April 14, 2017 illumos