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Re: raid10 hard disk choice

From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Matthew Wakeling <matthew(at)flymine(dot)org>, pgsql-performance(at)postgresql(dot)org
Subject: Re: raid10 hard disk choice
Date: 2009-05-21 21:41:05
Message-ID: dcc563d10905211441j57f6fa5es6694b3c192dee446@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
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.

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