Re: Advice configuring ServeRAID 8k for performance

On Thursday, August 05, 2010, "Kenneth Cox" <kenstir(at)gmail(dot)com> wrote:
> 1) Should I switch to RAID 10 for performance? I see things like "RAID 5
> is bad for a DB" and "RAID 5 is slow with <= 6 drives" but I see little
> on RAID 6. RAID 6 was the original choice for more usable space with
> good redundancy. My current performance is 85MB/s write, 151 MB/s reads
> (using dd of 2xRAM per
> http://www.westnet.com/~gsmith/content/postgresql/pg-disktesting.htm).

If you can spare the drive space, go to RAID 10. RAID 5/6 usually look fine
on single-threaded sequential tests (unless your controller really sucks),
but in the real world with multiple processes doing random I/O RAID 10 will
go a lot further on the same drives. Plus your recovery time from disk
failures will be a lot faster.

If you can't spare the drive space ... you should buy more drives.

>
> 2) Should I configure the ext3 file system with noatime and/or
> data=writeback or data=ordered? My controller has a battery, the logical
> drive has write cache enabled (write-back), and the physical devices have
> write cache disabled (write-through).

noatime is fine but really minor filesystem options rarely show much impact.
My best performance comes from XFS filesystems created with stripe options
matching the underlying RAID array. Anything else is just a bonus.

> * I know "feels slow" is not scientific. What I mean is that any single
> query on a fact table, or any 'rm -rf' of a big directory sends disk
> utilization to 100% (measured with iostat -x 3).

.. and it should. Any modern system can peg a small disk array without much
effort. Disks are slow.

--
"No animals were harmed in the recording of this episode. We tried but that
damn monkey was just too fast."