Re: mdadm raid10 performance

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