gvinum raid5 performance seems slow

[R. B. Riddick]

--- Greg 'groggy' Lehey <grog at FreeBSD.org> 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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