Re: Disk arrangement in a cheap server

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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(at)blighty(dot)com
> <mailto:steve(at)blighty(dot)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(dot)pinto(dot)neto(at)gmail(dot)com
> <mailto:clodoaldo(dot)pinto(dot)neto(at)gmail(dot)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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