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Re: Looking for a cheap upgrade (RAID)

From: "scott(dot)marlowe" <scott(dot)marlowe(at)ihs(dot)com>
To: Chad Thompson <chad(at)weblinkservices(dot)com>
Cc: <josh(at)agliodbs(dot)com>,pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Looking for a cheap upgrade (RAID)
Date: 2003-05-02 21:20:56
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Seeing as you'll have 2 gigs of RAM, your swap partition is likely to grow 
cob webs, so where you put it probably isn't that critical.

What I usually do is say take 4 120 Gig drives, allocate 1 gig on each for 
swap, so you have 4 gigs swap (your swap should be larger than available 
memory in Linux for performance reasons) and the rest of the drives split 
so that say, the first 5 or so gigs of each is used to house most of the 
OS, and the rest for another RAID array hosting the database.  Since the 
root partition can't be on RAID5, you'd have to set up either a single 
drive or a mirror set to handle that.

With that setup, you'd have 15 Gigs for the OS, 4 gigs for swap, and about 
300 gigs for the database.  The nice thing about RAID 5 is that random 
read performance for parallel load gets better as you add drives.  Write 
performance gets a little better with more drives since it's likely that 
the drives you're writing to aren't the same ones being read.  

Since your swap os likely to never see much use, except for offline 
storage of long running processes that haven't been accessed recently, 
it's probably fine to put them on the same drive, but honestly, I've not 
found a great increase from drive configuration under IDE.  With SCSI, 
rearranging can make a bigger difference, maybe it's the better buss 
design, i don't know for sure.  Test them if you have the time now, you 
won't get to take apart a working machine after it's up to test it. :)

On Fri, 2 May 2003, Chad Thompson wrote:

> Can WAL and the swap partition be on the same drive?
> Thanks
> Chad
> ----- Original Message -----
> From: "Josh Berkus" <josh(at)agliodbs(dot)com>
> To: "Chad Thompson" <chad(at)weblinkservices(dot)com>; "pgsql-performance"
> <pgsql-performance(at)postgresql(dot)org>
> Sent: Friday, May 02, 2003 2:10 PM
> Subject: Re: [PERFORM] Looking for a cheap upgrade (RAID)
> Chad,
> > I realize that Im a raid on linux newbie so any suggestions are
> appreciated.
> > Im thinking I want to put this on an IDE Raid array, probably 0+1. IDE
> seems
> > to be cheap and effective these days.
> > What ive been able to glean from other postings is that I should have 3
> > drives, 2 for the database w/ striping and another for the WAL.
> Well, RAID 0+1 is only relevant if you have more than 2 drives.  Otherwise,
> it's just RAID 1 (which is a good choice for PostgreSQL).
> More disks is almost always better.  Putting WAL on a seperate (non-RAID)
> disk
> is usually a very good idea.
> > I would also appreciate raid hardware suggestions (brands, etc)
> > And as always im not afraid to RTFM if someone can point me to the FM :-)
> Use Linux Software RAID.    To get hardware RAID better than Linux Software
> RAID, you have to spend $800 or more.
> --
> -Josh Berkus
>  Aglio Database Solutions
>  San Francisco
> ---------------------------(end of broadcast)---------------------------
> TIP 5: Have you checked our extensive FAQ?

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