Provided by: flashcache-utils_3.1.3+git20150701-2ubuntu2_amd64 bug

NAME

       flashcache_create - create a new flashcache volume

DESCRIPTION

       flashcache_create  initializes  a new flashcache volume from unformated block devices.  It
       creates flashcache meta data and provides new volumes though their volume mappings.

SYNOPSIS

       flashcache_create -p back|around|thru [-s cache size] [-b block  size]  [-v]  cachedevname
       cache_devname disk_devname

OPTIONS

       -v     verbose

       -p     cache  mode.   Required  argument.   Specify  any  supported  option: (write-)back,
              (write-)thru or (write-)around.  Their respective implications are denoted below.

       -s     cache size.  Optional argument.  By default, flashcache will use the  auto-detected
              full  cache  device size.  When present, the given cache size is used instead.  The
              expected units are sectors, however any value can be suffixed by "k", "m" or "g" to
              interpret the argument in kilo-, mega- or gigabytes respectively.

       -b     block  size.   Optional  argument.   Defaults  to  4KB.  Must be a power of 2.  The
              default units is sectors.  However, k can be specified as unit type  as  well.   (A
              4KB blocksize is the correct choice for the vast majority of applications.

       -f     force  create.   Bypass  all  sanity checks (for example for the sector size).  Use
              with care.

CACHING MODES

       The following caching modes are supported:

       Writethrough (thru) - safest mode, all writes are cached to the cache device but are  also
       being written to disk immediately.  If the used cache device has a lower write performance
       than the backend disk (many early generation SSD drives manufactured between 2008-2010 are
       known  for  such a poor write performance) enabling the writethrough mode may decrease the
       system write performance.  All disk reads are cached (tunable through  flashcache's  /proc
       interface).

       Writearound  (ardound) - again, very safe, writes are not written to the cache device, but
       directly to the backend disk instead.  Disk blocks will only  be  cached  after  they  are
       read.  All disk reads are cached (tunable through flashcache's /proc interface).

       Writeback  (back)  -  fastest  mode  but  less  safe.   Writes only go to the cache device
       initially, and are being written to the backend disk later, depending on configured system
       policie.  All disk reads are cached (tunable through flashcache's /proc interface).

CACHE PERSISTENCE

       Writethru  and  Writearound caches are not persistent across a device removal or a reboot.
       Only Writeback caches are persistent across device removals and reboots.  This  reinforces
       'writeback is fastest', 'writethrough is safest'.

EXAMPLES

       flashcache_create -p back -s 1g -b 4k cachedev /dev/sdc /dev/sdb
              Creates  a  1GB  writeback  cache  volume with a 4KB block size on the cache device
              /dev/sdc to cache the disk volume /dev/sdb.  The name  of  the  device  created  is
              "cachedev".

       flashcache_create -p thru -s 2097152 -b 8 cachedev /dev/sdc /dev/sdb
              Same  as  above  but  creates a write through cache with units specified in sectors
              instead.  The name of the device created is "cachedev".

SEE ALSO

       flashcache_load(8), flashcache_destroy(8)

       README  and  other  documents  in  /usr/share/doc/flashcache-utils.   In  particular,  see
       flashcache-sa-guide.txt  for  configuring  the  flashcache kernel module through its /proc
       interface.

       The  flashcache   source   code   and   all   documentation   may   be   downloaded   from
       <https://github.com/facebook/flashcache/>.

AUTHORS

       Flashcache is developed by Mohan Srinivasan <mohan@fb.com>

       This  man page was written by Dmitry Smirnov <onlyjob@member.fsf.org> for Debian GNU/Linux
       (but may be used by others).