• Boaz Harrosh's avatar
    exofs: Multi-device mirror support · 04dc1e88
    Boaz Harrosh authored
    This patch changes on-disk format, it is accompanied with a parallel
    patch to mkfs.exofs that enables multi-device capabilities.
    
    After this patch, old exofs will refuse to mount a new formatted FS and
    new exofs will refuse an old format. This is done by moving the magic
    field offset inside the FSCB. A new FSCB *version* field was added. In
    the future, exofs will refuse to mount unmatched FSCB version. To
    up-grade or down-grade an exofs one must use mkfs.exofs --upgrade option
    before mounting.
    
    Introduced, a new object that contains a *device-table*. This object
    contains the default *data-map* and a linear array of devices
    information, which identifies the devices used in the filesystem. This
    object is only written to offline by mkfs.exofs. This is why it is kept
    separate from the FSCB, since the later is written to while mounted.
    
    Same partition number, same object number is used on all devices only
    the device varies.
    
    * define the new format, then load the device table on mount time make
      sure every thing is supported.
    
    * Change I/O engine to now support Mirror IO, .i.e write same data
      to multiple devices, read from a random device to spread the
      read-load from multiple clients (TODO: stripe read)
    
    Implementation notes:
     A few points introduced in previous patch should be mentioned here:
    
    * Special care was made so absolutlly all operation that have any chance
      of failing are done before any osd-request is executed. This is to
      minimize the need for a data consistency recovery, to only real IO
      errors.
    
    * Each IO state has a kref. It starts at 1, any osd-request executed
      will increment the kref, finally when all are executed the first ref
      is dropped. At IO-done, each request completion decrements the kref,
      the last one to return executes the internal _last_io() routine.
      _last_io() will call the registered io_state_done. On sync mode a
      caller does not supply a done method, indicating a synchronous
      request, the caller is put to sleep and a special io_state_done is
      registered that will awaken the caller. Though also in sync mode all
      operations are executed in parallel.
    Signed-off-by: default avatarBoaz Harrosh <bharrosh@panasas.com>
    04dc1e88
super.c 19.3 KB