RE: SCSI or IDE
Hello All
We have about a dozen production machines running software RAID1 with
IDE drives. We have experience going back about year now and we have
had a number of raid drive failures in that time.
Good points:
- If a drive fails, the machine carries on running and you can sort
it out the problem at a convenient time. You do not loose any data
and not much downtime.
Bad points:
- After a drive fails it is not guaranteed 100% that the box will be
bootable. If the bios supports booting off both IDE's it is a good
start but some combination of drive/contoller failures can leave the
machine unbootable. A cold reboot as opposed to a warm reboot can
make a difference. It is a good idea to have a boot stiffy available,
this should always work. At worst you may have to disable a drive in
the bios or open the case and swop the IDE cables to get it to boot.
- If you have a "glitch" on a drive the raid will mark the partition
as defective possibly when there is no permanent damage. You have to
reboot the server before you can attempt to bring this partition back
on line. Once rebooted you can attempt to re-sync the drives. If you
loose sync again in the next few hours, start planning on replacing
the drive. But I have had a partition drop out, re-booted the
machine, re-synced and it worked faultlessly for months. So it is
definitely worth considering this before you replace the drive.
- You cannot "hot swap" the drives.
Bottom line is I would much rather have a machine with software raid
1 than one drive alone. Most of the new machines we build have this
configuration.
However if guaranteed 24/7 operation if your requirement, as opposed
to security of data and minimizing downtime then you will have to buy
something exotic that supports hot-swap and has a good reputation.
I have also played with machines with cheap bios based raid which
proved frustrating. I would much rather use Linux software raid than
any of these.
Be very careful to set-up and check your cron scripts. If a drive
fails, you need the machine to send an e-mail to an address where you
know it is going to be read and acted upon! You do not want that e-
mail buried in 1000 other system warnings that get deleted without
being read.
Have fun.
Ian
On 28 Nov 2002 at 14:15, Jones, Steven wrote:
> If you lose the primary boot disk on software raid its not bootable in my
> experience.
>
> I wouldnt use software raid for any prod box for this reason.
>
> I happen to have 2 x 20g sitting, and since I only need 2 gig ish
> max..........
>
> Steven
>
> -----Original Message-----
> From: Russell Coker [mailto:russell@coker.com.au]
> Sent: Thursday, 28 November 2002 1:35
> To: Jones, Steven; 'Thomas Kirk'
> Cc: debian-isp@lists.debian.org
> Subject: Re: SCSI or IDE
>
>
> On Wed, 27 Nov 2002 23:30, Jones, Steven wrote:
> >
> http://www.promise.com/product/product_detail_eng.asp?productId=93&familyId
> >= 7
> >
> > i was actually looking at one of these.
> >
> > For my simpler needs, data protection is important but there isnt lots of
> > it so 2 x 20 gig disks mirrored is heaps. I would like to keep the uptime
> > up, so was thinking of this solution, anybody tried one? Its for my web
> > server with all of a 128k connection so sucky performance isnt an issue as
> > its bugger all hits.
>
> If you only need RAID-1 then software RAID is probably best. It's cheapest
> and provides much better performance than most hardware RAID's. Also if you
>
> only need 20G of storage then you still may want to consider 120G drives,
> they are much faster than 20G drives.
>
> > However for another job Im thinking of elsewhere (a 2 node cluster) though
> > it would be a disaster. 3meg a sec just wont cut it, i can get 16 meg off
> a
> > second hand scsi setup for the same dosh.
>
> You can get 40 meg from a software RAID-1 on IDE drives more easily and
> cheaply.
>
> --
> http://www.coker.com.au/selinux/ My NSA Security Enhanced Linux packages
> http://www.coker.com.au/bonnie++/ Bonnie++ hard drive benchmark
> http://www.coker.com.au/postal/ Postal SMTP/POP benchmark
> http://www.coker.com.au/~russell/ My home page
>
>
> --
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Ian Forbes ZSD
http://www.zsd.co.za
Office: +27 21 683-1388 Fax: +27 21 674-1106
Snail Mail: P.O. Box 46827, Glosderry, 7702, South Africa
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