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SNMETADUMP(1)                                                                                  SNMETADUMP(1)



NAME
       snmetadump - Save and process a copy of the Xsan File System metadata

SYNOPSIS
       snmetadump -d [-c] [-bF] [-D <n>] [-f dump_file] __FsName__

       snmetadump -a [-m [-s [-M]]] [-bF] [-D <n>] [-f dump_file] __FsName__

       snmetadump -r [-bF] [-D <n>] [-f dump_file] __FsName__

       snmetadump -j journal_file...  [-bF] [-D <n>] [-f dump_file] __FsName__

       snmetadump -x [-bF] [-D <n>] [-f dump_file] __FsName__

       snmetadump -X [-bF] [-D <n>] [-f dump_file] __FsName__

DESCRIPTION
       The  snmetadump  utility  provides  the  ability  to  create a copy of the volume metadata for use in
       restoring a volume after a disaster. If some portion of the Xsan volume is lost, the volume  metadata
       can be restored from a copy of the metadata dump file.

       In  a  managed  Xsan environment the metadata is kept up to date using special restore journal files.
       These restore journals describe the metadata updates that must be applied to a metadata dump to bring
       the dump up to date with the current volume metadata. In the case of a disaster and metadata recovery
       all managed files on the volume will be restored as long as they had been stored to  tape.  When  the
       volume is accessed after the metadata has been restored all files are in the "tape-only" state, mean-ing meaning
       ing that the file will contain the data of the last copy stored. On a managed volume the  process  of
       keeping a metadata dump up to date by applying restore journal files is performed by the daily backup
       processing.

NON-MANAGED USAGE
       A Xsan metadata dump has limited uses in a non-managed environment. On a non-managed volume the  dump
       only  matches the state of the metadata until the volume manager (FSM) process is started. After this
       point metadata and data will have changed and the dump file is out of date. However, saving a copy of
       the  metadata  is  valuable  during  significant volume or hardware configuration changes, and during
       software upgrades. If accidental misconfiguration or data loss is encountered the metadata  dump  can
       be used to restore the state of the metadata.

       To create an snmetadump manually:

       1.     Stop the FSM.

       2.     If  feasible,  run cvfsck to verify the correctness of the metadata.  This may take a signifi-cant significant
              cant amount of time depending on file system size and speed.

       3.     Run snmetadump -cd __FsName__ to create a new metadump.  This may take a significant amount of
              time depending on file system size and speed.

       4.     Restart the FSM.

       If an issue arises requiring restoration of metadata, the following procedure should be used:

       1.     Restore  the  original  file  system configuration file that was present when the metadump was
              created.

       2.     Prepare the metadump for restore: snmetadump -am __FsName__

       3.     Restore the metadump: snmetadump -r [-f dump_file] __FsName__

       Note that if restore journals are not enabled, restoring a metadump will cause any  changes  to  file
       system metadata made after the metadump was created to be lost.

       The metadump is only useful for restoring the state of the metadata given a valid, consistent config-uration configuration
       uration file.  It will not roll back configuration changes or repair broken configurations.

METADATA RESIZING
       The preferred way of expanding a volume is by adding stripe  groups  using  the  cvupdatefs  utility.
       However, in some scenarios it is necessary to resize existing stripe groups.  In particular, this may
       be necessary when recovering from a disk array failure where the replacement disk array  is  not  the
       same size as the original.  The snmetadump utility provides a limited mechanism to allow this.

       The  replacement  stripe  groups may have a different number of LUNs in them and those LUNs may be of
       different sizes than the original LUNs.  No other aspect of the stripe  group  configuration  may  be
       changed or data loss may result.

       In particular, the stripe breadth of the stripe groups cannot be altered during restore, so it is im-portant important
       portant that the original stripe breadth value is still suitable for the altered stripe group or per-formance performance
       formance degradation may result.

       If decreasing the size of stripe groups is required, the __FsName__.usage report file in the metadump
       directory should be consulted.  This report file is updated every  time  snmetadump  applies  restore
       journals  and  indicates  the minimum size that each stripe group could be decreased to, based on the
       existing data in the stripe group.

       To restore metadata to stripe groups that have been resized by changing the size  of  the  LUNs,  the
       number of LUNs, or both:

       1.     Create  a  backup  copy of the volume configuration file and the metadump file.  Restore these
              files if the resize operation should fail or need to be aborted for any reason.

       2.     Run snmetadump -a __FsName__ to optimize the metadump.

       3.     Alter the volume configuration file to include the desired LUNs in each stripe group.  Do  not
              alter the number of stripe groups or any other aspect of the storage layout.

       4.     Run  snmetadump  -a  -s -m -M __FsName__ to prepare the metadump for metadata restore when the
              size or number of metadata disks has changed. The -M option disables the truncation  of  files
              for file systems where StorageManager or SnPolicy is enabled. File truncation is necessary and
              would normally occur when preparing the metadump for restore in disaster recovery. So  if  the
              resizing of metadata disks is in conjunction with disaster recovery, do not use the -M option.

       5.     Run snmetadump -r __FsName__ to restore the metadump.

       6.     Run cvfsck to verify correctness of the restored metadata. (Recommended)

NOTES
       When saving a copy of the metadata it is recommended that copies of the  volume  configuration  files
       are saved too.

       It is always recommended that cvfsck(1) is run before a metadata dump is saved. This will ensure that
       there are no metadata inconsistencies copied to the metadata dump.

       WARNING: Incorrect usage of this utility can result in data loss. Always refer to the Xsan documenta-tion documentation
       tion before using this utility.

USAGE
       -a     Apply  Metadata  Changes  -  apply completed restore journals to the metadump and optimize the
              dump.   This option will also close the current restore journal, open a new  restore  journal,
              then  locate  and apply the restore journals that need to be applied to the metadata dump. The
              backup process will invoke snmetadump with this option as part of the nightly backup on a man-aged managed
              aged  volume.   This operation must be performed in order for storage manager to read the dump
              file.

       -b     Display the build information for this binary

       -c     This option can only be run with the -d option.  Clean up metadata dump, restore  journal  and
              temporary  files associated with a volume. When a new metadata dump is generated, previous re-store restore
              store journals are no longer needed or valid. When invoked with this option,  snmetadump  will
              check  the  metadump  directory for files to clean up.  This option cannot be undone, so it is
              recommended that all existing dump and restore journal files be backed up prior to  execution.

       -d     Dump Metadata - Read in the volume metadata and save a copy to a metadata dump file. This file
              can later be used to replace lost metadata in the case of system failure.   The  FSM  must  be
              stopped  while  the  metadata dump is performed.  It is recommended to use cvfsck to check the
              consistency of the metadata before creating a new metadump where feasible.

       -D <n> Turn on debugging flags (useful for support personnel only).

       -f dump_file
              Specify the name of the dump file to create or process. If no -f argument is  given  then  the
              default  dump  file  will be used. The default is /Library/Logs/Xsan/database/metadumps/metad-ump.VolName. /Library/Logs/Xsan/database/metadumps/metadump.VolName.
              ump.VolName.

       -F     Force the operation. Override the state of a meta-dump which is  undetermined  or  potentially
              incomplete. Only use this flag at the recommendation of StorNext technical support.

       -j journal_file
              Apply  the  specified restore journal to the metadata dump.  NOTE: Normally, this option would
              be used only if there is a journal that needs to be applied  manually  just  prior  to  volume
              restoration.  This option is needed only if a journal needs to be applied outside of normal -a
              processing. After using -j to apply a journal, snmetadump can no longer track  which  journals
              have  or need to be applied, so either the metadata dump must be used to restore the volume or
              a new metadump needs to be created.

       -m     Prepare a metadata dump for restore.  The -m flag must be provided with the -a flag.   If  the
              file system configuration indicates storageManager is enabled, this process will also truncate
              all files to allow for retrieval from tape after the restoration process.

       -r     Restore Metadata - Read metadata state from the dump file and  rebuild  the  volume  metadata.
              Metadump  must  be prepared for restore using the -m flag before restoring.  All Xsan binaries
              and configuration files must be restored before this step can be processed.

       -s     Resize Stripe Groups - Modify the metadump to reflect modified stripe group sizes in the  con-figuration configuration
              figuration  file.   Must  be  used during restore preparation in conjunction with the -m flag.
              See above.

       -x     Examine a metadata dump - Verify the format of the metadata dump

       -X     Test the metadump status to verify that the metadump is valid and usable by snmetadump. In ad-dition addition
              dition  this check will test the metadump version to ensure that the metadump file is compati-ble compatible
              ble with this version of snmetadump. If the metadump is usable snmetadump  will  exit  with  a
              status of 0. If the metadump is not usable snmetadump will exit with a status of 1.

MORE NOTES
       On  a managed volume it is important to note that snmetadump is a single piece of a larger backup and
       restore procedure. Be sure to refer to the Xsan documentation before attempting to use this  utility.

       Incorrect usage of this utility may result in data loss.

       The snmetadump utility depends on adequate free metadata space to recover file system metadata. It is
       recommended that managed Xsan file system use exclusive metadata stripe groups to prevent data  files
       from  taking up needed metadata space. In the case where the snmetadump utility determines that there
       is not enough metadata space to manage disaster recovery snmetadump will fail and recommend  that  an
       additional  metadata stripe group be added. See the cvupdatefs(1) man page for more details on adding
       stripe groups.

RETURN VALUES
          0 - Success
          1 - Failure - There was an error processing the metadata dump
          2 - Dump Busy - The dump is being processed by another instance of
                snmetadump. Try again later. See MORE NOTES section.

FILES
       /Library/Logs/Xsan/database/metadumps/
              Default location of metadump files for managed file systems

       /Library/Logs/Xsan/data/VolName/
              Default location of metadump files for unmanaged file systems

       metadump.VolName
              Metadump file

       metadump.VolName.lock
              Temporary file lock for metadump file

       restore_journal-VolName.seqno.*
              Restore journal files.

       VolName.usage
              Metadump resizing report.  See above.

SEE ALSO
       snfs_config(5), cvmkfile(1), cvfsck(1), cvupdatefs(1), cvadmin(1)



Xsan File System                                December 2005                                  SNMETADUMP(1)