Re: mdadm raid10 performance

[Keld Jørn Simonsen <keld@xxxxxxxx>]

On Mon, Jun 02, 2008 at 02:47:53AM +0600, ???? ????????? wrote:
> Hello. I have a simple question.
> 
> I just created mdadm raid10 with four disks. The raid  build process
> complete successfully.
> All of 4 HDD are connected with separate SATA wires directly to motherboard.
> The mode of operation (selected in bios) neither AHCI nor RAID.
> 
> I decide to acheive performance information of software RAID.
> So I read 10 blocks by 64Mb. This give me roughly performance of one disk.
> (I expect that it will be 4x speed ! it should read from 4 hdd
> simultaneously!!!, BUT NOT! )
> 
> So, second test were reading 10 blocks (from 0 to 9) in one process,
> and 10 blocks (from 10 to 19) in second thread.
> I acheive performance of half disk... in each thread.
> 
> WTF? maybe raid is configured incorrectly ? Or my tests are invalid ?
> 
> Any ideas ?

have a look on the howto performance section.

http://linux-raid.osdl.org/index.php/Performance

the far layout is "far" better:-)

Also note the problem solving section there.

doing IO in more threads will have your array behave in random read
mode. 

What kernel are you running?

best regards
keld
--
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