[Bug 349] New: stripped MD0 splits requests incorrectly

[Martin J. Bligh]

http://bugme.osdl.org/show_bug.cgi?id=349

           Summary: stripped MD0 splits requests incorrectly
    Kernel Version: See 2.5.4x upto 2.5.60
            Status: NEW
          Severity: blocking
             Owner: [e-mail]
         Submitter: [e-mail]

Distribution: SuSE 8.1
Hardware Environment: Two disk RAID on adaptec SCSI 
Software Environment: XFS on MD0 (stripped) on two SCSI disks
Problem Description:

When trying to mount an XF  S system on such a RAID system and XFS replays
its log its hits BIO_BUG_ON(!bio->bi_io_vec) in ll_rw_block:submit_bio.

According to axboe the problem is that MD splits requests incorrectly. It
needs to ensure that when splitting requests between each resulting
subrequest is at least one page long. 0 length BIOs as generated here are
illegal.

Fixing requires extended surgery in the MD request splitting.