[CentOS] XFS and LVM2 (possibly in the scenario of snapshots)
pasik at iki.fi
Sun Dec 13 15:15:07 UTC 2009
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.
"Barriers are now supported by all the types of dm devices."
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