Re: Optimal settings for RAID controller - optimized for writes

Hi,

I don't have PERC H710 raid controller, but I think he would like to know raid
striping/chunk size or read/write cache ratio in writeback-cache setting is the
best. I'd like to know it, too:)

Regards,
--
Mitsumasa KONDO
NTT Open Source Software Center

(2014/02/18 0:54), Tomas Vondra wrote:
> The thing is, it's difficult to transfer these experiences without clear
> idea of the workloads.
>
> For example I wouldn't say 200 updates / second is a write-heavy workload.
> A single 15k drive should handle that just fine, assuming the data fit
> into RAM (which seems to be the case, but maybe I got that wrong).
>
> Niels, what amounts of data are we talking about? What is the total
> database size? How much data are you updating? Are those updates random,
> or are you updating a lot of data in a sequential manner? How did you
> determine UPDATEs are the bottleneck?
>
> Tomas
>
> On 17 Únor 2014, 16:29, DFE wrote:
>> Hi,
>> I configured a similar architecture some months ago and this is the best
>> choice after some pgbench and Bonnie++ tests.
>> Server: DELL R720d
>> CPU: dual Xeon 8-core
>> RAM: 32GB ECC
>> Controller PERC H710
>> Disks:
>> 2xSSD (MLC) Raid1 for Operating System (CentOS 6.4)
>> 4xSSD (SLC) Raid10 for WAL archive and a dedicated "fast tablespace",
>> where
>> we have most UPDATE actions (+ Hot spare).
>> 10xHDD 15kRPM Raid5 for "default tablespace" (optimized for space, instead
>> of Raid10)  (+ Hot spare).
>>
>> Our application have above 200 UPDATE /sec. (on the "fast tablespace") and
>> above 15GB per die of records (on the "default tablespace").
>>
>> After the testing phase I had the following conclusion:
>> 4xSSD (SLC) RAID 10 vs. 10xHDD RAID 5 have comparable I/O performance in
>> the sequential Read and Write, but much more performance on the Random
>> scan
>> (obviously!!), BUT as far I know the postgresql I/O processes are not
>> heavily involved in a random I/O, so at same price I will prefer to buy
>> 10xHDD instead of 4xSSD (SLC) using above 10x of available space at the
>> same price!!
>>
>> 10xHDD RAID 10 vs. 10xHDD RAID 5 : with Bonnie++ I noticed a very small
>> difference in I/O performance so I decided to use RAID 5 + a dedicated Hot
>> Spare instead of a RAID10.
>>
>> If I could go back,  I would have spent the money of the SLC in other
>> HDDs.