Re: Disk arrangement in a cheap server

On Nov 24, 2007, at 8:17 AM, Ron Johnson wrote:

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> On 11/24/07 09:12, Scott Marlowe wrote:
>> On Nov 24, 2007 5:09 AM, Clodoaldo
>> <clodoaldo.pinto.neto@gmail.com> wrote:
>>> I will build a cheap server and I'm in doubt about what would the
>>> the
>>> best for performance:
>>>
>>> 1 - everything in one lonely fast 10,000 rpm Raptor HD;
>>>
>>> 2 - two cheap 7,200 rpm 16MB cache HDs like this:
>>>
>>>     disk 1 - system and pg_xlog

This doesn't really buy you much. The supposed advantage of having
pg_xlog on its own drive is so that the head doesn't need to seek. If
it's on the system drive it'll be competing with, at least, syslog.

>>>     disk 2 - pg_data without pg_xlog
>>>     or a better arrange suggested by you;
>>>
>>> 3 - The two cheap HDs above in Raid 0.
>>
>> From a DBA perspective, none of those seem like a good choice, as
>> there's no redundancy.
>>
>> I'd make the two 7200 RPM drives a RAID-1 and have some redundancy so
>> a single disk failure wouldn't lose all my data.  then I'd start
>> buying more drives and a good RAID controller if I needed more
>> performance.

It depends on what the box is used for, but for most cases where the
data
is valuable, that sounds like a much better idea.

For batch data crunching, where the data is loaded from elsewhere then
processed and reported on, the cost of losing the data is very low, and
the value of the machine is increased by RAID0-ing the drives to make
the crunching faster... RAID0 could be good. That's probably not the
case
here.

>
> Remember: disks are *cheap*.  Spend an extra US$250 and buy a couple
> of 500GB drives for RAID 1.  You don't mention what OS you'll use,
> but if you really need cheap then XP & Linux do sw RAID, and FreeBSD
> probably does too.
>

Disks aren't necessarily cheap. Disks are fairly expensive, especially
when you need more spindles than will fit into the servers chassis
and you
need to move to external storage. Disk n+1 is very expensive, likely
more expensive than the cheap 1U server you started with.

Two, though, does seem to be false economy for a server that'll be
running a database, when you can get a 1U chassis that'll take 4 drives
pretty cheaply.

Cheers,
   Steve