On Fri, Dec 11, 2009 at 12:10:59AM +0800, 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. > https://www.redhat.com/archives/dm-devel/2009-December/msg00079.html "Barriers are now supported by all the types of dm devices." -- Pasi