Re: Postgresql 9.0.6 Raid 5 or not please help.

Thanks for all. I change to RAID 1 and here is new pg_bench result:

pgbench -h 127.0.0.1 -p 5433 -U postgres -c 10 -T 1800 -s 10 pgbench
Scale option ignored, using pgbench_branches table count = 10
starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 10
query mode: simple
number of clients: 10
number of threads: 1
duration: 1800 s
number of transactions actually processed: 4373177
tps = 2429.396876 (including connections establishing)
tps = 2429.675016 (excluding connections establishing)
Press any key to continue . . .

Tuan Hoang ANh
On Fri, Dec 23, 2011 at 10:25 PM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>wrote:

> On Fri, Dec 23, 2011 at 5:15 AM, alexandre - aldeia digital
> <adaldeia(at)gmail(dot)com> wrote:
> >> I'm not so confident that a RAID-1 will win over a single disk. When it
> >> comes to writes, the latency should be ~50 higher (if both disk must
> >> sync), since the spindles are not running synchronously. This applies to
> >> softraid, not something like a battery-backend raid controller of
> course.
> >>
> >> Or am I wrong here?
> >>
> >
> > Software RAID-1 in Linux, can read data in all disks and generally
> increase
> > a lot the data rate in reads. In writes, for sure, the overhead is great
> > compared with a single disk, but not too much.
>
> Exactly. Unless you spend a great deal of time writing data out to
> the disks, the faster reads will more than make up for a tiny increase
> in latency for the writes to the drives.
>
> As regards the other recommendation in this thread to use two mirror
> sets one for xlog and one for everything else, unless you're doing a
> lot of writing, it's often still a winner to just run one big 4 disk
> RAID-10.
>
> Of course the real winner is to put a hardware RAID controller with
> battery backed cache between your OS and the hard drives, then the
> performance of even just a pair of drives in RAID-1 will be quite
> fast.
>
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