What are ASM's?

This Wiki is brought to you by Backup Central, where you can find the Mr. Backup Blog, Forums, and a mailing list for each forum!
Backup FAQs	Service Providers	Backup Software	Backup Hardware	Backup Book Wiki	Free Stuff	Miscellaneous

ASM is a NetWorker acronym that stands for Application Specific Module. There are 2 kinds of ASMs: internal and external. ASMs may also be either complete ASMs, or wrapper ASMs.

Internal ASM's are written in C and are compiled into the save and recover programs. These ASMs are triggered by the standard directives that you can find on the NetWorker server. You may also use these ASMs yourself if you create your own directives.

External ASMs are either C programs or scripts that call the nsrfile program. External ASMs generate data on their own (i.e. using tar, cat, or other program) and send it to NetWorker using the nsrfile tool.

Complete ASMs both send data to the NetWorker server at save time, and receive data from the server at restore time. Examples of this type of ASM are logasm and mailasm.

Wrapper ASMs perform an operation on a block of data before it is sent to NetWorker. Examples of wrapper ASMs are the PosixCRC32 ASM or the Xlate ASM.

The "uasm" manual page contains information about all internal ASMs. The list of internal ASMs from the UASM(8) manual page:

     always The always ASM always performs a back up of a file,
             independent of the change time of the file.

      atimeasm
             The atimeasm is used to backup files without chang-
             ing  the access time of the file.  This functional-
             ity is a  subset  of  mailasm.   On  most  systems,
             atimeasm uses the file mtime for selection and then
             resets the  file  atime  after  the  backup  (which
             changes  the  file ctime).  On systems that support
             interfaces for maintaining the file  atime  without
             changing  the  file  ctime, atimeasm has no effect,
             since the file atime is normally preserved.

      compressasm
             The compressasm uses a software  compression  algo-
             rithm  to  compress  file  data.  This ASM does not
             compress directories.  The  amount  of  compression
             achieved  is data-dependent.  compressasm uses con-
             siderable amounts of CPU resources, so its benefits
             may be limited on low-powered systems.

      holey  The holey ASM handles holes or blocks of zeros when
             backing up files and preserves these  holes  during
             recovery.   On  some  filesystems interfaces can be
             used to find out the location of file hole informa-
             tion.   Otherwise,  blocks  of  zeros that are read
             from the file are skipped.  This  ASM  is  normally
             applied  automatically  and  does  not  need not be
             specified.

      logasm The logasm enables file changes during backup  ses-
             sions.   logasm  can  be  used  for "log" files and
             other similar files where a file changes  during  a
             backup operation is not worth noting.

      mailasm
             The  mailasm uses mail-style file locking and main-
             tains the access time of a  file,  preserving  "new
             mail has arrived" flag on most mail handlers.

      mtimeasm
             The mtimeasm is used to backup files using the file
             mtime for file selection instead of the file ctime.

      nsrindexasm
             The  nsrindexasm  is used to recover from NetWorker
             file index backups performed prior  to  Version  6.
             During  recovery  from  these  older index backups,
             nsrindexasm is invoked automatically by  nsrck  and
             mmrecov.

      nsrmmdbasm
             The nsrmmdbasm is used to process NetWorker's media
             index. Normally, nsrmmdbasm  is  invoked  automati-
             cally  by  savegrp  and  mmrecov, and should not be
             used in NetWorker directives.

      null   The null ASM does not back up the  specified  files
             and  directories,  but  keeps  the file name in the
             online index of the parent directory.

     nullasm
             nullasm is an alternate  name  for  the  null  ASM,
             named   for  backward  compatibility  with  earlier
             releases where nullasm was  a  separate  executable
             program instead of an internal ASM.

      posixcrcasm
             The  posixcrcasm  is used to calculate a 32-bit CRC
             for a file during a backup.   This  CRC  is  stored
             along  with  the file and is verified when the file
             is restored;  no  verification  occurs  during  the
             backup  itself.   Using  this ASM it is possible to
             validate a file at restore time, but  it  does  not
             provide a way to correct any detected errors.

      rawasm The  rawasm  is  used  to back up /dev entries (for
             example, block- and  character-special  files)  and
             their  associated raw disk partition data.  On some
             systems, /dev entries are actually  symbolic  links
             to device specific names. Unlike other ASMs, rawasm
             follows symlinks, allowing the shorter /dev name to
             be  configured.   When  recovering, rawasm requires
            that the filesystem node for the raw  device  exist
             prior  to  the recovery.  This protects against the
             recovery of a /dev entry  and  the  overwriting  of
             data  on  a  reconfigured disk.  You can create the
             /dev entry, having it refer to a different raw par-
             tition,  and force an overwrite if desired.  If you
             create the /dev entry as a symbolic link, the  data
             is  recovered  to  the target of the symbolic link.
             Precautions should be taken when using rawasm,  see
             the CAVEATS section.
             the CAVEATS section.

      skip   The  skip  ASM does not back up the specified files
             and directories, and does not place the filename in
             the online index of the parent directory.

      swapasm
             The  swapasm  does not backup actual file data, but
             recreates a zero-filled file of the correct size on
             recovery.   This  ASM  is used on systems where the
             swapping device is a swap file that must be  recov-
             ered with the correct size, but the contents of the
             swap file are not important and do not need  to  be
             backed up.

      xlateasm
             The  xlateasm  translates  file  data  so that data
             backed up is not immediately recognizable.