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).