[mythtv-users] Horrendous RAID-6 performance

[John Drescher]

On Fri, Mar 28, 2008 at 5:51 PM, Yan Seiner <yan at seiner.com> wrote:
>
>  John Drescher
>
>
>  > can you post the output of cat /proc/mdstat
>
>  OK, see below.  All of the system stuff sits on two SCSI drives.  The
>  array with bad performance consists of 6-400 GB SATA drives.  They only
>  have a single 1.2 TB partition.
>
>  selene:/var/log# cat /proc/mdstat
>  Personalities : [raid0] [raid1] [raid6] [raid5] [raid4]
>  md10 : active raid6 sdd1[0] sdi1[5] sdh1[4] sdg1[3] sdf1[2] sde1[1]
>       1562834944 blocks level 6, 64k chunk, algorithm 2 [6/6] [UUUUUU]
>
My first guess was the system was resyncing the array. That is
obviously not the case.

Here at work I have a few similar amd systems with 6 320GB sata2
Seagate 7200.10 drives in linux software raid 6 and I get around
260MB/s where you get 3.

 # hdparm -tT /dev/md1

/dev/md1:
 Timing cached reads:   2388 MB in  2.00 seconds = 1193.69 MB/sec
 Timing buffered disk reads:  786 MB in  3.00 seconds = 261.88 MB/sec

Can you post the output of cat /proc/interrupts?

And  blockdev --report

Are you sure that nothing else is using to the disks at the moment you
ran hdparm?

John