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

NAME

     zdb -- Display zpool debugging and consistency information

SYNOPSIS

     zdb [-CumdibcsDvhLMXFPA] [-e [-p path...]] [-t txg] [-U cache] [-I inflight I/Os] [-x dumpdir] poolname [object ...]
     zdb [-divPA] [-e [-p path...]] [-U cache] dataset [object ...]
     zdb -m [-MLXFPA] [-t txg] [-e [-p path...]] [-U cache] poolname
     zdb -R [-A] [-e [-p path...]] [-U cache] poolname poolname vdev:offset:size[:flags]
     zdb -S [-AP] [-e [-p path...]] [-U cache] poolname 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 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
     invocations is not documented, a knowledge of ZFS internals is assumed.

     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 refer-
	     enced (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 con-
	     tiguous 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.

     -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.

     -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 avail-
	     able uberblocks and their associated transaction numbers.

     -U cachefile
	     Use a cache file other than /boot/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.

     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)

AUTHORS

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

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

BSD
								   July 26, 2014							       BSD