Raid5, Raid0, Seagate 7200.10 - Uneven read speads

[Faldaani]

Hello

Setup is as follows:
2.6GHZ C2D on a Gigabyte 965P-DS4
2gb PC-6400 DDR2
8x 250gb 7200.9 Seagate HD's running on the mobo controller in various software raid setups that aren't important.

Areca 1220 controller
8x 500gb 7200.10 16mb cache Seagate HD's, firmware revision 3.AAK. (SATA)

4 of the 500gb disks, serials 5QG1**** are running in Raid5 on the Areca controller
3 of the 500gb disks, serials 9QG1**** are running in Raid0 on the same controller.
1 of them is being RMA'd :P

These are the HD Tach results, with 32mb zones selected for the raid 5 array.
http://marc01.bsnet.se/r5.png

These are the results for the Raid0 array with the same settings.
http://marc01.bsnet.se/r0.png

The arrays are used for video storage and are using 128k stripe size and 64k cluster size. The Areca controller is set to use SATA 300 with NCQ. The disks have the "limit to 1.5gpbs operation" jumper removed. Read ahead cache on the controller is enabled.

Why does the graph look like an EKG readout?

(Raid0 array will get replaced by Raid5 once RMA'd disk gets here, don't worry :P)

[drizzt81]

can you disable the controller's cache? Try that and see if it changes the charts.

+2 points for using PNG images. Thanks :)

[unhappy_mage]

That looks like it averages out to about what I'd expect from that array. Probably caching or something is making it jump around like that.

The real question, though, is application performance. If that's problematic right now, then play with settings until it goes away. But if it works, why break it?

[Faldaani]

Raid 5 with cache off
http://marc01.bsnet.se/r5_nocache.png

Well, at least its fairly even, but slow. Is 40mb/sec what one would expect to get without cache turned on?

EDIT: As to why break it? Well, it annoys me, hehe.