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

     zdb -- display ZFS	storage	pool debugging and consistency information

     zdb [-AbcdDFGhikLMNPsvXYy]	[-e [-V] [-p path]a|] [-I inflight I/Os] [-o
	 var=value]a| [-t txg] [-U cache] [-x dumpdir]
	 [poolname[/dataset | objset ID]] [object|rangea|]
     zdb [-AdiPv] [-e [-V] [-p path]a|]	[-U cache] poolname[/dataset | objset
	 ID] [object|rangea|]
     zdb -C [-A] [-U cache]
     zdb -E [-A] word0:word1:a|:word15
     zdb -l [-Aqu] device
     zdb -m [-AFLPXY] [-e [-V] [-p path]a|] [-t	txg] [-U cache]	poolname [vdev
     zdb -O dataset path
     zdb -r dataset path destination
     zdb -R [-A] [-e [-V] [-p path]a|] [-U cache] poolname
     zdb -S [-AP] [-e [-V] [-p path]a|]	[-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
     not a fsck(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

     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	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
	     count.  See -N for	determining if [poolname[/dataset | objset
	     ID]] is to	use the	specified [dataset | objset ID]	as a string
	     (dataset name) or a number	(objset	ID) when datasets have numeric

	     If	specified multiple times provides greater and greater ver-

	     If	object IDs or object ID	ranges are specified, display informa-
	     tion about	those specific objects or ranges only.

	     An	object ID range	is specified in	terms of a colon-separated tu-
	     ple of the	form <start>:<end>[:<flags>].  The fields start	and
	     end are integer object identifiers	that denote the	upper and
	     lower bounds of the range.	 An end	value of -1 specifies a	range
	     with no upper bound.  The flags field optionally specifies	a set
	     of	flags, described below,	that control which object types	are
	     dumped.  By default, all object types are dumped.	A minus	sign
	     (-) negates the effect of the flag	that follows it	and has	no ef-
	     fect unless preceded by the A flag.  For example, the range
	     0:-1:A-d will dump	all object types except	for directories.

	     A	     Dump all objects (this is the default)
	     d	     Dump ZFS directory	objects
	     f	     Dump ZFS plain file objects
	     m	     Dump SPA space map	objects
	     z	     Dump ZAP objects
	     -	     Negate the	effect of next flag

     -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:a|: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 and L2ARC header from	the specified device.
	     zdb -l will return	0 if valid label was found, 1 if error oc-
	     curred, 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 de-
	     fault, 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.

     -N	     Same as -d	but force zdb to interpret the [dataset	| objset ID]
	     in	[poolname[/dataset | objset ID]] as a numeric objset ID.

     -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	dataset	path destination
	     Copy the specified	path inside of the dataset to the specified
	     destination.  Specified path must be relative to the root of
	     dataset.  This option can be combined with	-v for increasing ver-

     -R	poolname vdev:offset:[lsize/]psize[: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 physical	size, or logical size /	physical size) of the
	     block to read and,	optionally, flags (a set of flags, described

	     b offset  Print block pointer at hex offset
	     c	       Calculate and display checksums
	     d	       Decompress the block.  Set environment variable
		       ZDB_NO_ZLE to skip zle when guessing.
	     e	       Byte swap the block
	     g	       Dump gang block header
	     i	       Dump indirect block
	     r	       Dump raw	uninterpreted block data
	     v	       Verbose output for guessing compression algorithm

     -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]a|
	     Operate on	an exported pool, not present in /etc/zfs/zpool.cache.
	     The -p flag specifies the path under which	devices	are to be

     -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 _a|
	     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, e.g.
	     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.

     -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.

     -Y	     Attempt all possible combinations when reconstructing indirect
	     split blocks.  This flag disables the individual I/O deadman
	     timer in order to allow as	much time as required for the at-
	     tempted reconstruction.

     -y	     Perform validation	for livelists that are being deleted.  Scans
	     through the livelist and metaslabs, checking for duplicate	en-
	     tries and compares	the two, checking for potential	double frees.
	     If	it encounters issues, warnings will be printed,	but the	com-
	     mand will not necessarily fail.

     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)

FreeBSD	13.0			October	7, 2020			  FreeBSD 13.0


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