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Re: XFS and RAID5

To: Seth Mos <knuffie@xxxxxxxxx>
Subject: Re: XFS and RAID5
From: Justin Tripp <jtripp@xxxxxxxx>
Date: Mon, 18 Jun 2001 08:21:19 -0600 (MDT)
Cc: Andrew Klaassen <ak@xxxxxxx>, <linux-xfs@xxxxxxxxxxx>
In-reply-to: <4.3.2.7.2.20010618153515.02d29138@xxxxxxxxxxxxx>
Sender: owner-linux-xfs@xxxxxxxxxxx
I have used both the 3ware and Promise Raid solutions.  Their are two
Promise RAID cards.  Only one will work with linux and it is a software
raid solution.  Promise only supports RedHat 6.1,6.2 and Suse 6.2, and
only the basic kernels in those releases.  So, if you are not interested
in XFS, then you could try them out.  It is likely, though, that you could
get the same performance (and cheaper), but just buying a additional
promise IDE controller and running the kernel's software raid on top of
that.  And then you could run any kernel you desired to -- plus XFS.  IDE
software RAID is not likely to have too great of performance.  (FYI
Promise's kernel driver is not open source, only part of it is and I never
did get them to return any emails I sent them about using the card under
linux).

3ware, on the other hand, is a hardware raid.  As far as your computer is
concerned you have a SCSI controller hooked to a pci slot.  The overhead
of IDE disks is not seen by the processor since it only interacts with the
Raid controller and cannot see the individual disks.  I have a 3ware
controller with 4 40G disks running RAID 5 with XFS as the underlying
filesystem.  It works quite well.

3ware did have problems with the firmware and RAID5, but these have been
fixed and can easily be obtained from their website.  The problems only
occured if the RAID ran in degraded mode, and if one did not have a disk
failure, then the problem never occurred. (Phew).  The kernel driver
works well in the 2.2 kernels, but 3ware is not too keen on helping you
run in 2.4.  Now that some distributions ship with 2.4, they may be
changing their minds, but... Nonetheless, their driver is open source and
is part of the kernel tree.  The driver I am running is cut out of the
2.4.5-ac5 patch and applied to a 2.4.5 cvs version of XFS.  I have not had
any problems despite the fact that XFS seems to exercise the underlying
hardware more than ext2 does.

I believe the 3ware card is a reasonably cheap way to get a 100+G raid.
But I did have to do some light kernel hacking to get everything working
reasonably well.

                                        .justin.

On Mon, 18 Jun 2001, Seth Mos wrote:

> At 09:13 18-6-2001 -0400, Andrew Klaassen wrote:
> >On Mon, Jun 18, 2001 at 03:55:36PM +1000,
> >Robin Humble wrote:
> >
> > > Around the time of the 2.4.3 kernel we used XFS over software
> > > RAID5 for a month or so before a disk died and we didn't
> > > bother replacing it - we've been using 420G (7 disks) of RAID0
> > > since with zero problems. RAID5 seemed ok and we sorted out
> > > any initial performance problems as we found them with the
> > > super-responsive XFS people on this list.
> >
> >7 disks?  I'm curious: SCSI or IDE?  (We're looking into a
> >Promise or 3ware card to allow us to put lots of IDE drives in a
> >box and run software RAID over top, and were wondering if anyone
> >else has had experience with these cards+software RAID+XFS.)
>
> IIRC the 3ware driver is a bit shakey. The 3ware card is a hardware raid
> solution and not a software one. If you use promise cards you will probably
> use software raid.
>
> The issue with the 3ware raid was firmware related. If the controller was
> missing a disk and running in  degraded mode file system corruption could
> and would occur.
> Other then that it is a fine IDE raid controller.
>
>
> >Andrew Klaassen
>
> Good luck
> --
> Seth
> Every program has two purposes one for which
> it was written and another for which it wasn't
> I use the last kind.
>
>


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