On Thu, Aug 5, 2010 at 12:28 PM, Kenneth Cox <kenstir@gmail.com> wrote:
> I am using PostgreSQL 8.3.7 on a dedicated IBM 3660 with 24GB RAM running
> CentOS 5.4 x86_64. I have a ServeRAID 8k controller with 6 SATA 7500RPM
> disks in RAID 6, and for the OLAP workload it feels* slow. I have 6 more
> disks to add, and the RAID has to be rebuilt in any case, but first I would
> like to solicit general advice. I know that's little data to go on, and I
> believe in the scientific method, but in this case I don't have the time to
> make many iterations.
>
> My questions are simple, but in my reading I have not been able to find
> definitive answers:
>
> 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).
Sequential read / write is not very useful for a database benchmark.
It does kind of give you a baseline for throughput, but most db access
is mixed enough that random access becomes the important measurement.
RAID6 is basically RAID5 with a hot spare already built into the
array. This makes rebuild less of an issue since you can reduce the
spare io used to rebuild the array to something really small.
However, it's in the same performance ballpark as RAID 5 with the
accompanying write performance penalty.
RAID-10 is pretty much the only way to go for a DB, and if you need
more space, you need more or bigger drives, not RAID-5/6
--
To understand recursion, one must first understand recursion.