[arch-general] mdadm: RAID-5 performance sucks

Karol Babioch karol at babioch.de
Wed Apr 10 08:18:27 EDT 2013


I guess I was too vague with some of the details regarding the setup, so
I will try to be more specific now.

Am 09.04.2013 18:20, schrieb Chris Down:
> I assume you're using Linux software RAID


> I've experienced this when using RAID6 and a suboptimal stripe cache
> size.

I already have tinkered with the stripe cache size, but probably should
approach this more systematically. I've found a "tuning" script at [1],
but although it increased performance on Ubuntu by a bit, it hadn't any
impact on Arch :(.

Am 10.04.2013 02:35, schrieb Rafa Griman:
> What filesystem?


> What "benchmark" are you running?

Simple and plain "old" dd, just as described at [2].

> Stripe size?

In both cases the chunk size is 512K, which is quite big, but it is
primarily used for video files and works with Ubuntu just fine.

> HDDs connected to a PCI(e|X) RAID controller or on board controller?

Its an onboard controller. To be more specific, this is what lspci says:

00:1f.2 SATA controller: Intel Corporation 6 Series/C200 Series Chipset
Family SATA AHCI Controller (rev 05)

> Those 70 MB/s and 35 MB/s are from a client node or local?

I've measured them in both cases (Arch & Ubuntu) locally, but from a
client I get very similar results.

> If they're from a client node, what are you using: FTP, SAMBA, NFS, ...?

I've only tried SMB so far, but given the fact that the results are bad
as they are locally, it shouldn't matter here.

> Config files?

Which ones? Pretty much everything is measured out of the box, partially
even using the live environments, so I haven't configured too much at
all. As said I've played around with the sysctl settings, but haven't
configured anything else that should matter here.

Best regards,
Karol Babioch

[1]: http://ubuntuforums.org/showthread.php?t=1494846
[2]: https://wiki.archlinux.org/index.php/SSD_Benchmarking#Using_dd

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