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From: Daniel Janzon <daniel.janzon@edgeware.tv>
To: "linux-lvm@redhat.com" <linux-lvm@redhat.com>
Subject: [linux-lvm] Best way to run LVM over multiple SW RAIDs?
Date: Tue, 29 Oct 2019 08:47:29 +0000	[thread overview]
Message-ID: <A8A53B0E4B7ACF4BAD5C77D3671AC8976AB85B3B@EX01.edgeware.tv> (raw)

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Hello,

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 ensure that data is spread well over the drive to guarantee a good worst-case performance. With linear allocation rather than striped, if load is directed to files on the first PV (a SW RAID) the system is again exposed to the 1-core limitation.

I tried "--stripes 8 --stripesize 512", and would appreciate any ideas of other things to try. I guess the performance hit can be in the file system as well. I tried XFS and EXT4 with default settings.

Kind Regards,
Daniel


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             reply	other threads:[~2019-10-29  8:47 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-29  8:47 Daniel Janzon [this message]
2019-12-07 16:16 ` [linux-lvm] Best way to run LVM over multiple SW RAIDs? 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
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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