Re: bad performance on RAID 5

[Bill Davidsen <davidsen@tmr.com>]

Sevrin Robstad wrote:
> I've tried to increase the cache size - I can't measure any 
> difference.....

You probably won't help small writes, but large writes will go faster 
with a stripe cache of size num_disks*chunk_size*2 or larger.
>
> Raz Ben-Jehuda(caro) wrote:
>> did u  increase the stripe cache size ?
>>
>>
>> On 1/18/07, Justin Piszcz <jpiszcz@lucidpixels.com> wrote:
>>> Sevrin Robstad wrote:
>>> > I'm suffering from bad performance on my RAID5.
>>> >
>>> > a "echo check >/sys/block/md0/md/sync_action"
>>> >
>>> > gives a speed at only about 5000K/sec , and HIGH load average :
>>> >
>>> > # uptime
>>> > 20:03:55 up 8 days, 19:55,  1 user,  load average: 11.70, 4.04, 1.52
>>> >
>>> > kernel is 2.6.18.1.2257.fc5
>>> > mdadm is v2.5.5
>>> >
>>> > the system consist of an athlon XP1,2GHz and two Sil3114 4port S-ATA
>>> > PCI cards with a total of 6  250gb S-ATA drives connected.
>>> >
>>> > [root@compaq ~]# mdadm --detail /dev/md0
>>> > /dev/md0:
>>> >        Version : 00.90.03
>>> >  Creation Time : Tue Dec  5 00:33:01 2006
>>> >     Raid Level : raid5
>>> >     Array Size : 1218931200 (1162.46 GiB 1248.19 GB)
>>> >    Device Size : 243786240 (232.49 GiB 249.64 GB)
>>> >   Raid Devices : 6
>>> >  Total Devices : 6
>>> > Preferred Minor : 0
>>> >    Persistence : Superblock is persistent
>>> >
>>> >    Update Time : Wed Jan 17 23:14:39 2007
>>> >          State : clean
>>> > Active Devices : 6
>>> > Working Devices : 6
>>> > Failed Devices : 0
>>> >  Spare Devices : 0
>>> >
>>> >         Layout : left-symmetric
>>> >     Chunk Size : 256K
>>> >
>>> >           UUID : 27dce477:6f45d11b:77377d08:732fa0e6
>>> >         Events : 0.58
>>> >
>>> >    Number   Major   Minor   RaidDevice State
>>> >       0       8        1        0      active sync   /dev/sda1
>>> >       1       8       17        1      active sync   /dev/sdb1
>>> >       2       8       33        2      active sync   /dev/sdc1
>>> >       3       8       49        3      active sync   /dev/sdd1
>>> >       4       8       65        4      active sync   /dev/sde1
>>> >       5       8       81        5      active sync   /dev/sdf1
>>> > [root@compaq ~]#
>>> >
>>> >
>>> > Sevrin
>>> > -
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>>>
>>> If they are on the PCI bus, that is about right, you probably should be
>>> getting 10-15MB/s, but it is about right.  If you had each drive on its
>>> own PCI-e controller, then you would get much faster speeds. 


-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979