Re: Horrible drive performance under concurrent i/o jobs (dlh problem?)

From: Nuno Silva (nuno.silva@vgertech.com)
Date: Thu Dec 19 2002 - 20:47:37 EST


Hello!

Torben Frey wrote:

[..snip..]

> watching "vmstat 1" in another window - and this is what surprised me:
> when I stopped the copy job, there were 22 more seconds when data was
> still written to the backup software raid. Is this a hint where the
> problem could be? I have the same "feature" when I write to my 3ware.
>

[..snip..]

AFAIK, this is because you have some GB of memory (RAM) that are beeing
used as disk-cache. It took 22 seconds for the cached writes-to-disk
being flushed to the device.

If 22 seconds is too much for the amount of cached disk-writes is
another story :)

Maybe 3ware controllers are slow with many disks? Try the same with only
3 disks to eliminate this variable.

Regards,
Nuno Silva

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