Il 08-12-2019 00:14 Stuart D. Gathman ha scritto:
On Sat, 7 Dec 2019, John Stoffel wrote:
The biggest harm to performance here is really the RAID5, and if you
can instead move to RAID 10 (mirror then stripe across mirrors) then
you should be a performance boost.
Yeah, That's what I do. RAID10, and use LVM to join together as JBOD.
I forgot about the raid 5 bottleneck part, sorry.
As Daniel says, he's got lots of disk load, but plenty of CPU, so the
single thread for RAID5 is a big bottleneck.
I assume he wants to use LVM so he can create volume(s) larger than
individual RAID5 volumes, so in that case, I'd probably just build a
regular non-striped LVM VG holding all your RAID5 disks. Hopefully
Wait, that's what I suggested!
If you can, I'd get more SSDs and move to RAID1+0 (RAID10) instead,
though you do have the problem where a double disk failure could kill
your data if it happens to both halves of a mirror.
No worse than raid5. In fact, better because the 2nd fault always
kills the raid5, but only has a 33% or less chance of killing the
raid10. (And in either case, it is usually just specific sectors,
not the entire drive, and other manual recovery techniques can come
into
play.)
While I agree with both (especially regarding RAID10), I propose another
setup: and MD RAID0 of the eight MD RAID5 arrays.
If I remember correctly, LVM striping code is based on device mapper
rather than MD RAID code. Maybe the latter is more efficient at striping
on fast NVMe drives?
Regards.
--
Danti Gionatan
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