From: Jonathan Briggs <jbriggs@esoft.com>
To: Reiserfs mail-list <Reiserfs-List@namesys.com>
Subject: SCSI caching and Reiser4
Date: Tue, 07 Mar 2006 10:37:14 -0700 [thread overview]
Message-ID: <1141753034.28859.13.camel@localhost> (raw)
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I thought I'd ask the list, since I've been wondering about it for a few
versions now, and I haven't been able to figure it out from the code
(although I haven't looked *that* hard).
My SCSI disks report that they have write back cache w/ FUA, which
should mean that write barriers work. Am I right?
But Reiser4 complains that it is disabling write barriers.
/dev/md2 is a RAID-0 of the two SCSI devices. I suspect that the MD
driver isn't supporting FUA properly but I haven't been able to figure
that out for sure.
Does anyone know for sure about MD block devices and write barriers?
Here are some of the interesting bits from dmesg:
Linux version 2.6.16-rc5-mm2 (jbriggs@oberon.rnd.esoft.com) (gcc version 4.0.2 20051125 (Red Hat 4.0.2-8)) #1 PREEMPT Fri Mar 3 14:06:12 MST 2006
...
SCSI device sda: 35843686 512-byte hdwr sectors (18352 MB)
sda: Write Protect is off
sda: Mode Sense: ab 00 10 08
SCSI device sda: drive cache: write back w/ FUA
SCSI device sda: 35843686 512-byte hdwr sectors (18352 MB)
sda: Write Protect is off
sda: Mode Sense: ab 00 10 08
SCSI device sda: drive cache: write back w/ FUA
sda: sda1 sda2 sda3 sda4
sd 0:0:0:0: Attached scsi disk sda
SCSI device sdb: 35843686 512-byte hdwr sectors (18352 MB)
sdb: Write Protect is off
sdb: Mode Sense: ab 00 10 08
SCSI device sdb: drive cache: write back w/ FUA
SCSI device sdb: 35843686 512-byte hdwr sectors (18352 MB)
sdb: Write Protect is off
sdb: Mode Sense: ab 00 10 08
SCSI device sdb: drive cache: write back w/ FUA
sdb: sdb1 sdb2 sdb3 sdb4
sd 0:0:1:0: Attached scsi disk sdb
...
md: Autodetecting RAID arrays.
md: autorun ...
md: considering sdb4 ...
md: adding sdb4 ...
md: sdb3 has different UUID to sdb4
md: sdb1 has different UUID to sdb4
md: adding sda4 ...
md: sda3 has different UUID to sdb4
md: sda1 has different UUID to sdb4
md: created md2
...
<5>reiser4[ktxnmgrd:md2:ru(1368)]: disable_write_barrier (fs/reiser4/wander.c:234)[zam-1055]:
NOTICE: md2 does not support write barriers, using synchronous write instead.
--
Jonathan Briggs <jbriggs@esoft.com>
eSoft, Inc.
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reply other threads:[~2006-03-07 17:37 UTC|newest]
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