Re: Optimal settings for RAID controller - optimized for writes

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.

2014-02-17 16:03 GMT+01:00 Niels Kristian Schjødt <
nielskristian(at)autouncle(dot)com>:

> Hi,
>
> I’m kind of a noob when it comes to setting up RAID controllers and
> tweaking them so I need some advice here.
>
> I’m just about to setup my newly rented DELL R720 12. gen server. It’s
> running a single Intel Xeon E5-2620 v.2 processor and 64GB ECC ram. I have
> installed 8 300GB SSDs in it. It has an PERC H710 raid controller (Based on
> the LSI SAS 2208 dual core ROC).
>
> Now my database should be optimized for writing. UPDATEs are by far my
> biggest bottleneck.
>
> Firstly: Should I just put all 8 drives in one single RAID 10 array, or
> would it be better to have the 6 of them in one RAID 10 array, and then the
> remaining two in a separate RAID 1 array e.g. for having WAL log dir on
> it’s own drives?
>
> Secondly: Now what settings should I pay attention to when setting this
> up, if I wan’t it to have optimal write performance (cache behavior, write
> back etc.)?
>
> THANKS!
>
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