[linux-lvm] write performance with active snapshot

[Stuart D. Gathman]

On Mon, 10 Nov 2008, Larry Dickson wrote:

> My guess is that you are getting the typical seek overhead. Have you tried
> making a volume group out of two separate RAID arrays (driving different
> spindles), and using lvdisplay --maps to make sure the parent volume is on
> one array, the snapshot(s) on the other?

At the expense of memory, LVM could copy larger pieces to snapshot on
write.  This would improve sequential write performance with snapshots
on the same spindle.  Is there a tuning knob for that?  Does read_ahead
affect COW?

-- 
	      Stuart D. Gathman <stuart at bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
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