Re: opinion on disk speed

On Thu, 2005-12-08 at 10:52, Vivek Khera wrote:
> I have a choice to make on a RAID enclosure:
>
> 14x 36GB 15kRPM ultra 320 SCSI drives
>
> OR
>
> 12x 72GB 10kRPM ultra 320 SCSI drives
>
> both would be configured into RAID 10 over two SCSI channels using a
> megaraid 320-2x card.
>
> My goal is speed. Either would provide more disk space than I would
> need over the next two years.
>
> The database does a good number of write transactions, and a decent
> number of sequential scans over the whole DB (about 60GB including
> indexes) for large reports.
>
> My only concern is the 10kRPM vs 15kRPM. The advantage of the 10k
> disks is that it would come from the same vendor as the systems to
> which it will be connected, making procurement easier.

I would say that the RAID controller and the amount of battery backed
cache will have a greater impact than the difference in seek times on
those two drives.

Also, having two more drives in the 15k category is likely to play to
its advantage more so than the speed of the drive spindles and seek
times. If you're worried about higher failures due to heat etc... you
could always make a couple of the drives spares.

Looking at the datasheet for the seagate 10k and 15k drives, it would
appear there is another difference, The 10k drives list a sustained
xfer rate of 39 to 80 MBytes / second, while the 15k drives list one of
58 to 96. That's quite a bit faster. So, sequential scans should be
faster as well.

Power consumption isn't much differnt, about a watt more for the 15ks,
so that's no big deal. I'd do a bit of googling to see if there are a
lot more horror stories with 15k drives than with the 10k ones.