Re: RAID 5 performance problems

[Ross Vandegrift <ross@willow.seitz.com>]

[CC list trimmed]

On Thu, Apr 03, 2003 at 10:05:27AM -0800, Peter L. Ashford wrote:
> > 4 of the raid HD's are connected to the Promise controller and the other
> > raid HD is master on the second onboard IDE channel (udma2/ATA33)
> 
> I've NEVER heard that the FastTrak runs fast (I have been told that they
> run VERY slowly).

The FastTrack cards are identical to the UltraDMA cards from promise -
you can turn one into the other with a resistor and a firmware flash.

> I've benchmarked RAW disk speeds with an Ultra-100 and
> WD1200JB drives, and gotten 50MB/S from each disk, as opposed to your
> 26MB/S (there should be almost no difference for the BB drives).

Makes perfect sense - he's getting 50M/s to each channel, but it's split
over two drives, so drive throughput is about halved.

> Use one disk per channel
> (Master only), and move the system disk onto one of the Promise cards.

Absolutely correct - you should *never* run IDE RAID on a channel that
has both a master and slave.  When one disk on an IDE channel has an
error, the whole channel is reset - this makes both disks inaccessible,
and RAID5 now has two failed disks => you data is gone!  *ALWAYS* use
separate IDE channels.


-- 
Ross Vandegrift
ross@willow.seitz.com

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