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 ([EMAIL PROTECTED]) (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 <[EMAIL PROTECTED]> eSoft, Inc.
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