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List:       linux-raid
Subject:    Re: RAID-0 Slowness
From:       Marc Mutz <Marc () Mutz ! com>
Date:       1999-06-30 20:03:03
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D. Lance Robinson wrote:
> 
> Try bumping your chunk-size up. I usually use 64. When this number is low,
> you cause more scsi requests to be performed than needed. If really big (
> >=256 ) RAID 0 won't help much.
> 
What if the chunk size matches ext2fs's group size (i.e. 8M)? This would
give very good read/write performance with moderatly large files (i.e.
<8M) if multiple processes do access the fs, because ext2fs usually
tries to store a file completely within one block group. The performance
gain would be n-fold, if n was the number of disks in the raid0 array
and the number of processes was higher than that.
It would give only single-speed (so to speak) for any given application,
though.
But then: Wouldn't linear append be essentially the same, given that
ext2fs spreads files all across the block groups from the beginning?

Would that not be the perfect setup for a web server's documents volume,
with MinServers==n? The files are usually small and there are usually
much more than n servers running simultaneously.

Is this analysis correct or does it contain flaws?
What be the difference between raid0 with 8M chunks and linear append?

Just my thoughts wandering off...

Marc

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