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From: Gionatan Danti <g.danti@assyoma.it>
To: LVM general discussion and development <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] Best way to run LVM over multiple SW RAIDs?
Date: Sun, 08 Dec 2019 12:57:36 +0100	[thread overview]
Message-ID: <4851bf1ac6d1dca625598bbfe3a28b8c@assyoma.it> (raw)
In-Reply-To: <alpine.LRH.2.21.1912071804540.9108@fairfax.gathman.org>

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
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8

  reply	other threads:[~2019-12-08 11:57 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-29  8:47 [linux-lvm] Best way to run LVM over multiple SW RAIDs? Daniel Janzon
2019-12-07 16:16 ` Anatoly Pugachev
2019-12-07 17:37   ` Roberto Fastec
2019-12-07 20:34     ` Stuart D. Gathman
2019-12-07 22:44       ` John Stoffel
2019-12-07 23:14         ` Stuart D. Gathman
2019-12-08 11:57           ` Gionatan Danti [this message]
2019-12-08 22:51           ` John Stoffel
2019-12-09 10:40         ` Guoqing Jiang
2019-12-09 10:26 Daniel Janzon
2019-12-09 14:26 ` Marian Csontos
2019-12-10 11:23 ` Gionatan Danti
2019-12-10 21:29   ` John Stoffel
2019-12-16  8:22 Daniel Janzon

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