Re: Software RAID checksum performance on 24 disks not even close to kernel reported

[Ole Tange <ole@xxxxxxxx>]

On Wed, Jun 6, 2012 at 6:05 PM, Igor M Podlesny <for.poige+lsr@xxxxxxxxx> wrote:
> On 6 June 2012 22:11, Ole Tange <ole@xxxxxxxx> wrote:
>> On Tue, Jun 5, 2012 at 1:14 AM, Ole Tange <ole@xxxxxxxx> wrote:
> […]
>> If the bottleneck is md0_raid6, choose a chunk size that gives
>> reasonable performance on your CPU (which in your case seem to be
>> 32-64 KB).
>
>   Which you're to never-ever do, since it's simply stupid to involve
> bunch of disks into so brief I/O ops.

Currently it seems the bottleneck is md0_raid6 running on one core as
it seems can only deliver 400 MB/s to a 24 disk RAID6. The hardware +
drivers supports 2000 MB/s according to the tests.

So without change the total bandwidth is 400 MB/s.

Let us say that we can change the config so md0_raid6 can deliver 600
MB/s, but at the cost that the hardware + drivers lose 2/3 of their
performance and thus can only deliver 650 MB/s. Then the total
bandwidth will be 600 MB/s.

To me what matters is the total performance, so I would choose the 600
MB/s over the 400 MB/s any day.

So Igor: Do you have numbers that back up your claim? Or do you advice
against it just because "it's simply stupid"?


/Ole
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html