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Date: Sat, 7 Dec 2019 15:34:53 -0500 (EST)
From: "Stuart D. Gathman" <stuart@gathman.org>
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Subject: Re: [linux-lvm] Best way to run LVM over multiple SW RAIDs?
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To: LVM general discussion and development <linux-lvm@redhat.com>

On Tue, Oct 29, 2019 at 12:14 PM Daniel Janzon <daniel.janzon@edgeware.tv> wrote:
> I have a server with very high load using four NVMe SSDs and
> therefore no HW RAID. Instead I used SW RAID with the mdadm tool.
> Using one RAID5 volume does not work well since the driver can only
> utilize one CPU core which spikes at 100% and harms performance.
> Therefore I created 8 partitions on each disk, and 8 RAID5s across
> the four disks.

> Now I want to bring them together with LVM. If I do not use a striped
> volume I get high performance (in expected magnitude according to disk
> specs). But when I use a striped volume, performance drops to a
> magnitude below. The reason I am looking for a striped setup is to

The mdadm layer already does the striping.  So doing it again in the LVM
layer completely screws it up.  You want plain JBOD (Just a Bunch
Of Disks).

-- 
 	      Stuart D. Gathman <stuart@gathman.org>
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.