Re: raid10 hard disk choice

On 5/21/09 2:41 PM, "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com> wrote:

> On Thu, May 21, 2009 at 2:29 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Thu, May 21, 2009 at 8:59 AM, Matthew Wakeling <matthew(at)flymine(dot)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.

From the original message:

" The server would not be only dedicated to postgresql but to be a file
server,
the rest of options like plenty of ram and battery backed cache raid card
are
done but this two different hard disk configuration have the same price and
i am
not sure what it is better."

So, with a write-back cache battery backed up raid card, xlog writes won't
be an issue.

>
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