Re: Disk arrangement in a cheap server - Mailing list pgsql-general

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On 11/25/07 01:28, Alex Turner wrote:
> Why the hell would you buy a 1U chassis in the first place when
> perfectly good cheap 4U chassis exists that will take 8 or more drives?
>
> 1U motherboards are a pain, 1U power supplies are a pain and 1U space
> for drives sucks.
>
> Most tests I've seen these days show that there is very little actual
> benefit from seperating pg_xlog and tablespace if you have a half decent
> controller card.  Infact you are better off putting it all on one nice
> RAID 10 to get the good read performance that splitting it up will loose.
>
> if you don't have a decent controller card, RAID 0 will suck too.
> Namely onboard SATA RAID often sucks.

pg_xlog and tablespaces should be on as much different hardware as
possible, to reduce the likelihood that a single part failure will
knock out both directory structures.

> Alex
>
> On Nov 24, 2007 12:06 PM, Steve Atkins < steve@blighty.com
> <mailto:steve@blighty.com>> wrote:
>
>
>     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
>     <mailto: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.

- --
Ron Johnson, Jr.
Jefferson LA  USA

%SYSTEM-F-FISH, my hovercraft is full of eels
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