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ZDB(8)			  BSD System Manager's Manual			ZDB(8)

     zdb -- Display zpool debugging and	consistency information

     zdb [-CumdibcsDvhLXFPA] [-e [-p path...]] [-t txg]	poolname [object ...]
     zdb [-divPA] [-e [-p path...]] dataset [object ...]
     zdb -m [-LXFPA] [-t txg] [-e [-p path...]]	poolname
     zdb -R [-A] [-e [-p path...]] poolname vdev:offset:size[:flags]
     zdb -S [-AP] [-e [-p path...]] poolname
     zdb -l [-uA] device
     zdb -C [-A] [-U cache]

     The zdb utility displays information about	a ZFS pool useful for debug-
     ging 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 invoca-
     tions is not documented, a	knowledge of ZFS internals is assumed.

     When operating on an imported and active pool it is possible, though un-
     likely, that zdb may interpret inconsistent pool data and behave errati-

     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 configura-
	     tion.  If specified multiple times	with -e	also display the con-
	     figuration	that would be used were	the pool to be imported.

     -d	     Display information about datasets. Specified once, displays ba-
	     sic dataset information: ID, create transaction, size, and	object

	     If	specified multiple times provides greater and greater ver-

	     If	object IDs are specified, display information about those spe-
	     cific objects only.

     -D	     Display deduplication statistics, including the deduplication ra-
	     tio (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 statis-
	     tics, showing the allocated (physically present on	disk) and ref-
	     erenced (logically	referenced in the pool)	block counts and sizes
	     by	reference count.

     -h	     Display pool history similar to zpool history, but	include	inter-
	     nal 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 op-
	     tion is also specified, also display the uberblocks on this de-

     -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 maximum
	     contiguous	free space and the percentage of free space in each
	     space map.	 When specified	three times display every spacemap

     -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,	band-
	     width, 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

     -F	     Attempt to	make an	unreadable pool	readable by trying progres-
	     sively older transactions.

     -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 num-

     -U	cachefile
	     Use a cache file other than /etc/zfs/zpool.cache.	This option is
	     only valid	with -C

     -v	     Enable verbosity.	Specify	multiple times for increased ver-

     -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.

     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

	 # 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

     zfs(8), zpool(8)

     This manual page is a mdoc(7) reimplementation of the illumos manual page
     zdb(1M), modified and customized for FreeBSD and licensed under the Com-
     mon Development and Distribution License (CDDL).

     The mdoc(7) implementation	of this	manual page was	initially written by
     Martin Matuska <> and
     Marcelo Araujo <>.

BSD				 May 10, 2012				   BSD


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