gvinum raid5 performance seems slow

[Steve Peterson]

Eric -- thanks for looking at my issue.  Here's a dd reading from one 
of the disks underlying the array (the others have basically the same 
performance):

$ time dd if=/dev/ad10 of=/dev/null bs=1m count=1000
1000+0 records in
1000+0 records out
1048576000 bytes transferred in 15.322421 secs (68434095 bytes/sec)
0.008u 0.506s 0:15.33 3.2%      20+2715k 0+0io 0pf+0w

and here's a dd reading from the raw gvinum device /dev/gvinum/vol1:

$ time dd if=/dev/gvinum/vol1 of=/dev/null bs=1m count=1000
1000+0 records in
1000+0 records out
1048576000 bytes transferred in 25.870684 secs (40531437 bytes/sec)
0.006u 0.552s 0:25.88 2.1%      23+3145k 0+0io 0pf+0w

Is there a way to nondestructively write to the raw disk or gvinum device?

For comparison, here's a read against the raw PATA device on the machine:

$ time dd if=/dev/ad0 of=/dev/null bs=1m count=1000
1000+0 records in
1000+0 records out
1048576000 bytes transferred in 26.096070 secs (40181376 bytes/sec)
0.013u 0.538s 0:26.10 2.0%      24+3322k 0+0io 0pf+0w

Steve


At 11:14 PM 10/27/2006, Eric Anderson wrote:
>On 10/27/06 18:03, Steve Peterson wrote:
>>I recently set up a media server for home use and decided to try 
>>the gvinum raid5 support to learn about it and see how it 
>>performs.  It seems slower than I'd expect -- a little under 
>>6MB/second, with about 50 IOs/drive/second -- and I'm trying to 
>>understand why.  Any assistance/pointers would be appreciated.
>>The disk system consists of 4 Seagate NL35 SATA ST3250623NS drives 
>>connected to a Promise TX4300 (PDC40719) controller, organized as a 
>>RAID5 volume via gvinum using this configuration:
>>drive drive01 device /dev/ad10
>>drive drive02 device /dev/ad6
>>drive drive03 device /dev/ad4
>>drive drive04 device /dev/ad8
>>volume vol1
>>    plex org raid5 256k
>>      sd length 200001m drive drive01
>>      sd length 200001m drive drive02
>>      sd length 200001m drive drive03
>>      sd length 200001m drive drive04
>>dd reports the following performance on a 1G file write to the 
>>RAID5 hosted volume:
>>$ time dd if=/dev/zero of=big.file bs=1m count=1000
>>1000+0 records in
>>1000+0 records out
>>1048576000 bytes transferred in 179.717742 secs (5834571 bytes/sec)
>>        179.76 real         0.02 user        16.60 sys
>>By comparison, creating the same file on the system disk (an old 
>>ATA ST380021A connected via a SIS 730 on the motherboard):
>>time dd if=/dev/zero of=big.file bs=1m count=1000
>>1000+0 records in
>>1000+0 records out
>>1048576000 bytes transferred in 28.264056 secs (37099275 bytes/sec)
>>         28.32 real         0.01 user        19.13 sys
>>and vmstat reports about 280-300 IOs/second to that drive.
>>The CPU is pretty weak -- an Athlon 750.  Is that the source of my 
>>problem?  If you look at the vmstat output below the machine is 
>>busy but not pegged.
>
>
>Try the dd to the raw gvinum device instead of through a filesystem, 
>and also to the individual disks.  That will at least tell us where to look.
>
>
>Eric
>
>
>
>--
>------------------------------------------------------------------------
>Eric Anderson        Sr. Systems Administrator        Centaur Technology
>Anything that works is better than anything that doesn't.
>------------------------------------------------------------------------
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