RAID on RedHat 3 ES

Thu Aug 19 19:43:50 UTC 2004

If you want some Dell specific information, there is a good Dell-Linux list
here:

Linux-PowerEdge at dell.com

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Regards, Marshall 

-----Original Message-----
From: Tobias Speckbacher [mailto:TSpeckbacher at quova.com] 
Sent: Thursday, August 19, 2004 2:33 PM
To: General Red Hat Linux discussion list
Subject: RE: RAID on RedHat 3 ES

> -----Original Message-----
> From: redhat-list-bounces at redhat.com [mailto:redhat-list-
> bounces at redhat.com] On Behalf Of kenwardc
> Sent: Thursday, August 19, 2004 10:48 AM
> To: 'General Red Hat Linux discussion list'
> Subject: RE: RAID on RedHat 3 ES
> 
> Hi Mike
> 
> Yep - the box is a Dell 1650 with Perc3 RAID on daughterboard so
> should be good for building the spare.

If you have a hardware raid controller the OS doesn't matter, as long as
the controller is supported.

Pretty decent description of various raid levels.

http://www.acnc.com/04_01_00.html

in short:

Raid 0 (stripe):  fast I/O, no fault tolerance. (min. 2 disks)
Raid 1 (mirror):  same I/O as single disk, fault tolerant (2 disks)
Raid 5 (stripe + parity): high read I/O, med write I/O, fault tolerant
(min 3 disks)
Raid 10 (mirror + stripe) : high overall I/O, same fault tolerance as
raid 1. (most expensive $/GB)

For a mail server, assuming you are not going to host a ton of users on
it in general RAID 1 serves best (given that you only have 2 drives).
If you can fork out money for 2 or 3 more drives I would go RAID 5 + 1
spare, maximizing fault tolerance and useable disk space.

Stripe is a definite no if you care about the uptime of the system and
recoverability from a disk failure without having to resort to tape
backups etc.

-T

> 
> Drives will be around 2 x 36 Gbyte so not too huge either.
> 
> Regards
> Chris
> 
> > -----Original Message-----
> > From: redhat-list-bounces at redhat.com
> > [mailto:redhat-list-bounces at redhat.com] On Behalf Of Michael Wimpee
> > Sent: 19 August 2004 18:39
> > To: General Red Hat Linux discussion list
> > Subject: Re: RAID on RedHat 3 ES
> >
> > On Thu, Aug 19, 2004 at 04:02:16AM -0500, Steve Phillips wrote:
> > >
> > > Software RAID comes with a preformance hit that with todays
> > processors
> > > you probably will never notice.
> > >
> > > RAID1 would be ok, if you are after rock solid redundancy then
> > > purchase another drive as a hot spare (and if your really
> > keen, try to
> > > ensure that the drives are nto from teh same production batch)
> > >
> > Be aware however, that under heavy I/O, a failed disk may take a
> > *really* long time to rebuild under software RAID. We saw
> > >150MB/s using four SCSI drives under software RAID 5, but
> > when testing rebuild speed, normal disk I/O caused the
> > rebuild time to get pushed out towards infinity. It wouldn't
> > have worked well in our situation so we went with a hardware
> > RAID controller.
> >
> > Mike Wimpee
> >
> > > comments like "dont know if it is really effective" are kinda
> wishy
> > > washy, effective against what ? was he saying that a single drive
> > > system would have greater redundancy than a mirrored setup
> > ? what sort
> > > of effect was he commenting on ?
> > >
> > > the preformance hit you will see will also depend on how many
> users
> > > and how busy you expect the server to be - also, buying
> > 5400rpm drives
> > > will probably not help much, try and get reasonably fast
> > drives with a
> > > reasonable ammount of cache ram.
> > >
> > > if you are after reliability only then there is no point to stripe
> 
> > > (infact, some people claim that software stripes actually
> > slow things
> > > down over say - RAID 10)
> > >
> > >
> > > --
> > > Steve.
> > >
> > > On Thu, 19 Aug 2004, kenwardc wrote:
> > >
> > > >Hi All
> > > >
> > > >Someone said to me today they didn't know whether RAID on
> > Linux was
> > > >very effective. Can someone tell me whether it's still
> > worth RAIDing
> > > >drives on Linux? I'm building a new mail server and I
> > wanted to put
> > > >in RAID 1 just in case of problems with drives etc. down the
> line.
> > > >Any advice appreciated.
> > > >
> > > >Also, provided the answer to the question is YES, is RAID
> > 1 the best
> > > >for a mail server or should I be looking at striping? I'm
> > obviously
> > > >not looking for the greatest speed but want absolutely reliable
> > > >redundancy.
> > > >
> > > >Regards
> > > >Chris
> > > >
> > > >
> > > >
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