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Dell 6800 PERC4 adapter: read/write cache

Posted on 2007-04-06
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Last Modified: 2008-09-13
I have Dell 6800 server with PERC4 Ultra320 SCSI RAID controller with 256 MB cache.

I did some tests and I have found, that this cache is probably divided to cca 240 MB read cache and only 7 MB write cache. I have used xdd test tool to bypass filesystem cache and I was able to read 240 MB files with very high transfer rate while with 245 MB files transfer rate dropped to about 30%. Write test showed this transfer rate drop when file size changed from 7 MB to 8 MB.

I'd like to increase write portion of the cache. I'm using command line utility named megarc to set controller parameters and I can't see any parameter, that could affect cache division.

Does anybody know, whether it is possible to change the size of write cache on PERC4 controller ?
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Question by:Jan Franek
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6 Comments
 
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by:BPiotrowski
ID: 18908490
Have you tried to set this in the Perc controller BIOS ? There should be a way to set the controller for how you want the cache to be divided - default I believe is 50/50.

-Bart
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by:Jan Franek
ID: 18916298
Hi Bart,
do you know, where in controller BIOS can be this setting ? I haven't found it yet.
Jan
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by:BPiotrowski
ID: 18917394
Are you able to get into the BIOS controller ? once you are in - on the virutal disk setting - there should be an allocation of cache - read/write percentage. Hmmm.. it may also be only if you create a new virtual disk....which is not going to help you. - Do you have the newest firmware for the raid controller ?
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by:Jan Franek
ID: 21247907
Sorry, I have forgotten, that this is still open.

I have upgraded firmware and BIOS too, but there's no way to change cache allocation. So probably the answer to my question is: No, it can't be done.
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