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

     zdb -- display zpool debugging and	consistency information

     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
     zdb -S [-AP] [-e [-V] [-p path ...]] [-U cache] poolname

     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 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 invoca-
     tions 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 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 (/boot/zfs/zpool.cache).  To specify the cache file to dis-
	     play, 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).

     -DD     Display a histogram of deduplication statistics, showing the al-
	     located (physically present on disk) and referenced (logically
	     referenced	in the pool) block counts and sizes by reference

     -DDD    Display the statistics independently for each deduplication ta-

     -DDDD   Dump the contents of the deduplication tables describing dupli-
	     cate 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	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.

     -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 from the specified device.  zdb -l will re-
	     turn 0 if valid label was found, 1	if error occurred, and 2 if no
	     valid labels were found.

	     If	the -q option is also specified, don't print the labels.

	     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.

     -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 in-
	     creasing 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, 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
	     /boot/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 di-
	     rectory.  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 progres-
	     sively 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 infor-

     -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	per-
	     formance 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 num-

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

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

     -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.

     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

     zfs(8), zpool(8)

FreeBSD	13.0		       October 06, 2017			  FreeBSD 13.0


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