NAME

       flashcache_create - create a new flashcache volume

DESCRIPTION

       flashcache_create  initializes  a new flashcache volume from unformated block devices.  It creates flash‐
       cache 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  de‐
              vice  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 be‐
       ing 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  flash‐
       cache-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/face‐
       book/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).

flashcache_create                                September 2011                             FLASHCACHE_CREATE(8)