Dissapointing performance of ciss RAID 0+1 ?

Ivan Voras ivoras at fer.hr
Thu Nov 9 10:17:23 UTC 2006

Pete French wrote:

> I've tried all the possible stripe sizes (128k gives the best performance)
> but still I only get the above speeds. Just one of the 15k drives on it's
> own performs better than this! I would expect the RAID-0 to give me at
> least some speedup, or in the worst case be the same, surely ?

The checklist for tuning usually goes like this:

- Is the controller cache enabled?
- Do you have the battery for it and is write cache enabled? (You won't 
make full use of the cache without the battery)
- How does your performance compare when using dd on the raw devices (in 
order: da0, da0s1, da0s1a...) vs when using it on the file system? (Poor 
performance might indicate FS vs stripe alignment issues)
- What does vmstat -i say while running your benchmarks? Any interrupt 
- If all of this fails, post dmesg, maybe someone will notice something 

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