[1490] in linux-scsi channel archive
Re: elevator sorting for the scsi subsystem.
daemon@ATHENA.MIT.EDU (Dario_Ballabio@milano.europe.dg.co)
Sun Mar 2 15:21:03 1997
Date: Sun, 2 Mar 1997 21:17:04 +0100
From: Dario_Ballabio@milano.europe.dg.com
To: linux-scsi@vger.rutgers.edu, lnz@dandelion.com
If a request writes sectors 2 and 3, filling with 1's the two blocks
and then another request writes sectorr 1 and 2 filling with 0's,
at the end sector 2 shoud be filled with 0's. If we sort the two
requests or if the drive reorder them, at the end sector 2 is
filled with 1's, which is not the expected result.
I cheched that there are (rare) cases of overlapping write requests
in normal operations, tipically at the very beginning of the
disk partition. My concern is that if we use simple queue tags
for write requests, cases as the above are likely to happen soon
or later, causing randomic disk corruptions.
I belive that we can safely sort write requests only provided that
there are no overlapping requests in the batch to be sorted.
In any case I would always use ordered queue tags for write requests.
db
