Richard first of all thank you for your time looking into this,
apricieting that.
What are my options from here? To move onto zvol with greater blocksize?
64k? 128k? Or I will get into another trouble going that way when I have
small reads coming from domU (ext3 with default blocksize of 4k)?
Richard Elling wrote:
On Feb 14, 2010, at 9:24 AM, Bogdan Ćulibrk wrote:
Greetings zfs-discuss@
I was trying to narrow this down for some quite time. The problem is resides on
couple of osol/sxce boxes that are used as dom0 hosts. Under high disk load on
domU guests (backup process for example) domU performance is terrible. The
worst thing is that iostat shows *very* high %w numbers, while zpool iostat
showing quite low numbers.
Where is iostat %w measured?
Couple things that to mention:
1. /etc/system tune: set zfs:zfs_arc_max = 524288000
2. dom0 is pinned to dedicated CPU, also memory is capped to 1GB.
3. no hardware raid involved, raw SATA drives fed to dom0 under rpool.
4. domUs are on top of zvols, 8K blocksize
5. iostat: http://pastebin.com/m4bf1c409
Is this data from dom0?
Looks like around 200-300 8KB random reads per second, which is
about all you can expect from 3-5 SATA disks.
-- richard
6. zpool iostat: http://pastebin.com/m179269e2
7. domU definition: http://pastebin.com/m48f18a76
8. dom0 bits are snv_115, snv_124, snv_126 and snv_130
9. domUs have ext3 mounted with: noatime,commit=120
10. there are ~4 domUs per dom0 host, each having dedicated cpu(s).
Any hint would be apreciated where should I go from here.
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