Re: more 10K disks or less 15K disks

Our experience shows that the 2.5 inch 10K disks have about the same
I/O rate as the 3.5 inch 15K disks. Ideal would be 15K 2.5 inch.

To answer you bigger question, it depends on how many threads are
running to perform the inserts. If you have lots (2-3 times as many threads
as disks) then your I/O will spread out over all of your disks, and you
can make use of all drives simultaneously.
If you have fewer threads than you have disks, then latency will be your limiting
factor, so the faster speed drives will be your best bet.

For a single thread, on 10K disks with only small write cache (256M) you will
probably only see approx 1500 random I/O per second. Bear in mind that a single database
transaction in postgres will use some number of threads, but require more than 1 I/O for
each transaction. You can probably tune it to achieve no more than 2,000 inserts per second
as a sustained rate.

If you have very few threads (5-10) then you will probably require some
fancier storage, such as solid state disk or at the very least very large (4-16GB)
write cache systems.

Evan.

Anj Adu wrote:
> I forgot to add that the 24 10K disks are 2.5 inch and the 12 15K
> disks are 3.5 inch
>
> On Wed, Apr 28, 2010 at 11:27 AM, Anj Adu <fotographs(at)gmail(dot)com> wrote:
>> I am faced with a hardware choice for a postgres data warehouse
>> (extremely high volume inserts..over 200 million records a day) with a
>> total storage of either
>>
>> 12 x 600G disks (15K) (the new Dell Poweredge C server)
>>
>> or
>>
>> 24 x 600G (10K disks)
>>
>> ALL direct attached storage.
>>
>> I am leaning toward the 24 disks as I expect the higher number of
>> disks to provide overall better performance under high loads
>>
>> Does anyone have any experience with a mixed 10K / 15K DAS storage
>> that you can share.
>>
>> Thank you
>>
>> Sriram