Chan Chung Hang Christopher wrote: > Mathieu Baudier wrote: > >>> LVM like md raid and drbd is a layered block device and >>> If you turn the wire caches off on the HDs then there is no problem, >>> but HDs aren't designed to perform to spec with the write cache >>> disabled they expect important data is written with FUA access (forced >>> unit access), so performance will be terrible. >>> >>> >> I hope that I'm not going too much off topic here, but I'm getting >> worried not to be sure to understand, especially when it has to do >> with data safety: >> >> Considering a stack of: >> - ext3 >> - on top of LVM2 >> - on top of software RAID1 >> - on top of regular SATA disks (no hardware RAID) >> is it "safe" to have the HD cache enabled? >> >> (Note: ext3, not XFS, hence the possible off-topic...) >> >> > > Nothing is safe once device-mapper is involved. > > >> In other words, is this discussion about barriers, etc. only relevant to XFS? >> > > No, it applies to all filesystems. Prior to barriers, fsync/fsyncdata > lies. See the man page for fsync. > No mention of barriers in the man page, I'm also getting confused. is device mapper used for software raid - i.e. /dev/mdX? If so what are the implications of barriers and where are they turned on / off? Forgive me for potential off topic, but I too run xfs on lvm which uses mapper.......risky?? > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos > -------------- next part -------------- A non-text attachment was scrubbed... Name: rkampen.vcf Type: text/x-vcard Size: 121 bytes Desc: not available URL: <http://lists.centos.org/pipermail/centos/attachments/20091210/cf20c7a5/attachment-0005.vcf>