Performance and cheap storage

[Greg A. Woods]

At Sun, 23 Jul 2006 13:28:10 -0400,
Wesley Craig wrote:
> 
> On 23 Jul 2006, at 11:00, Robert Banz wrote:
> > The second thing to consider is that the performance on modern SATA  
> > drives, if you're using a driver for the SATA interface that  
> > supports advanced features such as command queueing, are going to  
> > show you performance akin to SCSI drives -- even more so if you  
> > place them behind a 'quality' RAID subsystem that provides read/ 
> > write caching.
> 
> Another big win is providing independent IO channels for the  
> {configdirectory} and the mail store {partition}.  For instance, if  
> you're using an external SATA RAID for the {partition}, then using  
> the drives in the head for {configdirectory} can be a big win.  On  
> our systems, about 30% of our IO is to {configdirectory}.

(I'm going to have to think harder about moving {configdirectory} over
onto the RAID box!  I definitely see similar loads on my biggest system
too.)

Note that ready-to-use packaged RAID systems built from ATA and SATA
drives can be found for relatively little money -- certainly less than
the cost of equivalent bare high-end SCSI drives.

I've built a couple of systems now using Apple's Xserve RAID devices
with qlogic FC controllers on the host.  I don't know exactly how they
stand up today against similar hardware, but a couple years when they
were practially alone on the market they were significantly cheaper than
even the lowest-cost bare-bones SCSI-based FC RAID boxes, and orders of
magnitude cheaper than the big-boy systems like DEC/HP StorageWorks.

Now that everyone is in the SATA-based RAID market froogle.com is
showing me some rather decent prices that may even compete well with
Apple, though it looks like one must be very careful to compare units
with equal numbers of same-sized drives.  Lots are priced w/o drives.

One must also be careful to compare the transaction throughput
performance and cache sized on similar units.  The biggest selling point
of StoragWorks at the time I looked was that they had MUCH higher
transaction throughputs and thus would be far faster under the kinds of
loads that a large IMAP server might want to deliver.

Look on eBay for even better deals if you're willing to buy used gear.
(and why not?  often you can get two for far less than the price of one
and that gives you a full parts kit for your own repairs)

-- 
						Greg A. Woods

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