Re: Postgresql 9.0.6 Raid 5 or not please help.

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.