Re: raid10 hard disk choice

On Thu, May 21, 2009 at 2:29 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, May 21, 2009 at 8:59 AM, Matthew Wakeling <matthew@flymine.org> wrote:
>> On Thu, 21 May 2009, Linos wrote:
>>>
>>>        i have to buy a new server and in the budget i have (small) i have
>>> to select one of this two options:
>>>
>>> -4 sas 146gb 15k rpm raid10.
>>> -8 sas 146gb 10k rpm raid10.
>>
>> It depends what you are doing. I think in most situations, the second option
>> is better, but there may be a few situations where the reverse is true.
>
> One possible case of this - I believe that 15K drives will allow you
> to commit ~250 times per second (15K/60) vs. ~166 times per second
> (10K/60).  If you have a lot of small write transactions, this might
> be an issue.

But in a RAID-10 you aggreate pairs like RAID-0, so you could write
250(n/2) times per second on 15k where n=4 and 166(n/2) for 10k drives
where n=8.  So 500 versus 664... ?  Or am I getting it wrong.