Re: gvinum raid5 performance seems slow

--- Greg 'groggy' Lehey <grog@xxxxxxxxxxx> wrote:
"Sufficiently large data blocks" equates to several megabytes.
Currently MAXPHYS, the largest transfer request that would get to the
bio layer, is 131072 bytes. This would imply a stripe size of not
more than 32 kB for a five disk array, which is unrealistically small.

I did consider this optimization, but it would only work if Vinum were
first to buffer multiple requests, and there are all sorts of
reliability issues there. For example, you'd have to lie about the
first few requests that were only buffered and not actually sent out
to disk. Possibly it should be done anyway.

I did it that way in my graid5 class:
http://home.tiscali.de/cmdr_faako/geom_raid5.tbz

The source might look somehow incomprehensible, but it seems to be quite stable
(on amd64 and i386)...

I tried to benchmark with a 3 disk array:
Single disk: 30MB/sec write speed
graid5 device: 20MB/sec write speed

I would be interested in other benchmarks about it.

-Arne




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