topic Re: RAID cache in Disk Enclosures

RAID cache

Bernhard Mueller — Thu, 23 Dec 2004 10:24:51 GMT

Hi,

there is a SCSI RAID controller (A7143) in the machine which has the cache enabled (per sautil output) however, I wonder whether this is write-back or write-through?

looking at the saconfig man page there is no way of setting the cache to WBACK or WTRHU neither for a single LUN or all.

So I am afraid the controller is only capable of WTHRU. Is that correct?

Regards,
Bernhard

Re: RAID cache

David Bell_1 — Thu, 23 Dec 2004 10:35:48 GMT

Bernhard,

I'm not sure if this will help you but here it is:

http://docs.hp.com/en/J6369-90001/ch02s01.html

http://docs.hp.com/en/J6369-90001/J6369-90001.pdf

This describes the caching process but doesn't specifically mention WBACK or WTHRU.

HTH,

Dave

Re: RAID cache

Vincent Fleming — Thu, 23 Dec 2004 11:54:22 GMT

The (several) docs I found indicate a write-back cache. Some said just "256MB write cache", others just said "256MB cache", but the thing that makes me think it's pre-set to write-back is that it's ECC protected, battery-backed memory. Battery-backed is for write-back cache only - there's no point in using a battery with write-thru or read caches...

good luck,

Vince

Re: RAID cache

Bernhard Mueller — Wed, 29 Dec 2004 08:02:54 GMT

Vince,

that is what I assumed, however, performance on non-striped (two disk RAID1) LUNs made me doubt it.

My hope was that someone with HP internal sources of knowledge might have been able to clarify this.

Happy New Year!

Regards,
Bernhard