What is the output of hdparm /dev/hde and hdparm /dev/hdg? Especially of interest is whether multcount, using_dma and readahead are set to on. They can be automatically turned off by the kernel if there are any seek errors, like can happen early in the FC5 boot sequence with raid0. I have a patch to redhat nash to fix that if that is the case.
---------[ Received Mail Content ]----------
Subject : Poorer performance with Raid0 then without?
Date : Sat, 30 Dec 2006 23:07:48 -0800
From : "Listbox" <listbox@xxxxxxxxxxxxxx>
To : <ataraid-list@xxxxxxxxxx>
Hi folks!
I have been trying to use a
RAID bus controller: Silicon Image, Inc. PCI0680 Ultra ATA-133 Host
Controller (rev 02)
to create a RAID0 workspace for MythTV, but it's not working right....
I have two Seagate 160gb drives in a RAID 0 array on an SiI0680 PCI
ATA raid controller. I formatted an XFS filesystem on
/dev/mapper/sil_agbgdgbjfhei2,
and set mythbackend to use it. ( My DVB card is a DviCO
Fusion Gold 3,( Conexant CX23880).)
When I watch live MythTV, I get terrible artifacts on digital TV, and slow
frame rates on analog. When I reset mythbackend to use a ext3
partition on a single drive ( /dev/hdc1 ), performance is acceptable.
The RAID devices are hde and hdg, the/ partition is hdc.... to me this looks
like all my physical drives give comparable throughput. This is what hdparm
reports:
/dev/hda:
Timing cached reads: 1668 MB in 2.00 seconds = 834.10 MB/sec
Timing buffered disk reads: 88 MB in 3.05 seconds = 28.87 MB/sec
/dev/hde:
Timing cached reads: 1680 MB in 2.00 seconds = 838.49 MB/sec
Timing buffered disk reads: 168 MB in 3.03 seconds = 55.46 MB/sec
/dev/hdf:
Timing cached reads: 1688 MB in 2.00 seconds = 843.57 MB/sec
Timing buffered disk reads: 164 MB in 3.00 seconds = 54.59 MB/sec
/dev/hdg:
Timing cached reads: 1696 MB in 2.00 seconds = 846.68 MB/sec
Timing buffered disk reads: 162 MB in 3.03 seconds = 53.45 MB/sec
I also tried upping the PCI latency of the RAID card with
setpci -v -s 01:07.0 latency_timer=B0 # PCI0680 Ultra ATA-133 Host
But this had no effect. The DVB card has a latency of 32(decimal).
So, given the same hardware throughput, I would expect better performance
with the XFS+RAID setup. This is not the case. I went to considerable
trouble to get the RAID and XFS working on my Fedora 5 system, and it's
pretty discouraging to see that it actually
degrades instead of enhances performance.
I just reformatted with ext3, and tried again, and got the same degradation.
It's looking like the RAID is the problem, but I do not,NOT,NOT! want to
un-stripe the disks.
What else to try?
Listbox
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