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.
>
> regards.
