Provided by: zfsutils-linux_0.8.1-1ubuntu14_amd64 bug

NAME

     zdb — display zpool debugging and consistency information

SYNOPSIS

     zdb [-AbcdDFGhikLMPsvXY] [-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 [-AFLPXY] [-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 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 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 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. Each unique
             configuration is displayed only once.

     -ll device
             In addition display label space usage stats.

     -lll device
             Display every configuration, unique or not.

             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.
             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, 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 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. Set environment variable ZBD_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

     -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.

     -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 attempted reconstruction.

     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)