Re: Scsipi guru needed...

[Anders Magnusson <ragge%ludd.ltu.se@localhost>]

Michael L. Hitch wrote:
> On Sun, 30 Nov 2008, Anders Magnusson wrote:
> 
>> I have been trying to find out why the performance of the ciss
>> controller (Compaq raid) in
>> DL38x is really bad, but as I don't understand anything about the scsipi
>> layer (are there any docs?) I must ask around.  All this is really
>> strange.
>>
>> Writing data to the raw sd device (bs=64k) gets just over 7MB/s, which
>> is quite slow.
>> Some debugging showed that:
>> - A write transfer (from given to the ctlr to interrupt) takes 8ms. 
>> Ok, no write cache on the ctlr maybe?
> 
>   Does your controller have a battery backup?  I've found that without the
> battery backup, the controller does not use any write cache and write
> speeds are significantly reduced.
> 
No, it do not AFAIK.  But FreeBSD get good speed anyway, and I really doubt
that they fake a write cache.

-- Ragge