Software RAID-0 striping over Hardware RAID-5

Hi everyone,

I have a Xeon machine (3.06 Ghz single processor, 2 GB RAM, SuperMicro motherboard) with two 3ware 9500S-8 cards. I'm getting good performance with 3ware's Hardware RAID-5 (I have reasons why I don't want to use Software RAID-5 on this machine).

My question is, what kind of problems, if any, might I run into if I use Linux Software RAID to stripe the two RAID-5's together into a single RAID-0? The reason I'm thinking about doing this is to squeeze more performance out of the storage system for working with huge video files.

(BTW, this is what Apple does with its XSeve RAID in order to work with high definition video. The XServe has two 7-drive RAID-5 arrays, each connected to a fiber channel port. The data from both arrays goes into a single dual channel fiber channel card on a G5 workstation, which then uses software RAID-0 to stripe the two RAIDS together. )

With the 2.6 kernel (versions 2.6.6 and above), should I expect any trouble if a drive goes down on ONE of the RAID-5s and I have to replace the disk and rebuild? Will the much lower performance on one of the RAID 5s during rebuild cause problems for the RAID-0?

I guess it would be like making a RAID-0 with two drives of equal size, but very mismatched in terms of speed (i.e., a 4200 rpm drive and a 7200 rpm drive).

Words of wisdom would be appreciated.

Regards,
Andy Liebman

On Fri, 17 Sep 2004 at 6:03pm, [email protected] wrote

I have a couple of dual 3ware boxes I do this with, and have never had a problem. I would make sure that you have a hot spare on your RAID5 arrays, though. Because if one of them dies, you'll obviously lose everything on both arrays.

Joshua Baker-LePain
Department of Biomedical Engineering
Duke University