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

[Rafa Griman]

Hi :)

On Wed, Apr 10, 2013 at 2:18 PM, Karol Babioch <karol at babioch.de> wrote:
> Hi,
>
> 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
>
> Yes.
>
>> 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 :(.


So maybe could be an Arch issue. What about kernel versions, ...? Are
they the same in Ubuntu and Arch versions you're running?

Have you monitored CPU usage while you run dd? I find saidar
(libstatgrab) interesting to get a glimpse of what's happening
locally. sar can also be useful, ... Whole bunch of tools out there,
depends on your preferences ;)


> Am 10.04.2013 02:35, schrieb Rafa Griman:
>> What filesystem?
>
> ext4.
>
>> 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.


Was asking about the config files in case you were using Samba, but I
see it's not the case ;)

   Rafa