Re: RAID / SCSI / IDE Question - 2.9

[Nick Holland <nick@holland-consulting.net>]

Can you do RAID 1 with IDE?  Absolutely.

Can you do RAID 1 without a controller?  Yes, using RAIDframe.

Should you?  Weeeeell...depends.
What do you want the RAID for?  Continued up-time in the event of a
drive failure?  That translates very clearly to hardware RAID. 
Software RAID will HELP keep you from loosing data in the case of a
simple drive failure, but you can't count on it keeping you running
(esp. with IDE drives) in the event of a drive failure.  This is no
substitute for backups -- just an auxiliary.

Example:  You run backups nightly at 1:00am.  At 1:04am, a drive
failure occurs (this is HIGHLY likely, btw...not too much stresses a
disk like a backup).  So, at this point, you have a failed backup, and
a dead drive.  This means you have lost 24 hours of mail (you WERE
rotating your backups, right?).  A mirrored drive will have the last
24 hours of backup still there.  If you have HW mirroring, you are
probably still running, and you probably even got a good backup.  If
you have software mirroring, your incoming mail will be bouncing over
to your secondary MX (a very nice feature, and amazingly easy to
implement, btw) until you get the server repaired and rebuilt, but
(hopefully) nothing is lost.

However, if instead of a drive failure, you have a fire, a power
supply surge, theft, or other catastrophic event, you may loose both
drives, so your backups still need to be done.

Keep in mind that OpenBSD can not mirror the boot drive in software,
so if your boot drive fails, you have a problem.

I'm kinda partial to the ArcoIDE products (http://www.arcoide.com)
because they are completely software invisible, and because I have
failure-tested them, and know what they do when a drive suddenly fails
(something I argue everyone depending upon RAID should do).  The Arco
products are kinda "dumb" -- no speed benefit, nor a speed penalty. 
Other products exist which give performance benefits on read, like the
3ware products.  Another nice thing about the Arco products is that
should the RAID controller fail, you can just attach the drive
directly to the IDE interface on the computer and get right back up
and running.  You can also make a mirrored pair out of an existing
unmirrored drive -- these are two things that are uncertain in most HW
RAID 1 systems, and impossible in other RAID configurations.

Note: The often seen Promise FastTrack controllers are not true HW
RAID and are not supported by OpenBSD.

I've actually found some lawyers have a very realistic attitude about
computers: They should work for the users, not against them.  A level
of fault tollerance, or at least an understanding of what will happen
should ANY piece of a system fail, should be part of any system
design.  Sometimes the fault tollerance is just "We will tollerate any
problem until it is repaired", but that should be understood up
front.  Some failure points are very unlikely and very expensive to
"tollerate" in hardware, so for those points, the humans provide the
"tollerence", others are cheap and cost effective.  The defintion of
"cheap and cost effective" varies, of course. 8-)

Nick.

Martin Marconcini wrote:
> 
> Hello everybody:
> 
> I need a little bit of advice here; I have to setup two boxes (a third
> later)
> And need some advice about RAID. One will be the Mail Server. (Qmail)
> and even when it will handle less than 200 msg/day I need raid support
> on that box (1, mirror).
> 
> The question is can I do RAID 1 with IDE disks? Do I need a Controller?
> Can I do it w/out a controller? (i.e.: Software?) What would you
> recommend?
> 
> The problem is that since there are going to be two other boxes, I will
> also need raid on the web server and the firewall and SCSI disks are too
> expensive. (The main reason if Fault Tolerance, the customer is a
> Lawyer, and you know how I-don’t-like-computers lawyers are.) And the
> web/database server will be handling an internal application
> (php/mysql). Apart from backups I need it to be running 24/7 if
> possible. As you may know... downtime costs money.
> 
> There will be 20 workstations only, so load won't be a problem. (All
> PIII).
> 
> Thanks for your advice!
> 
> Regards,
> 
> Martin Marconcini
> www.marconcini.com.ar
> 
> "Life must be lived looking forward and can be understood only looking
> backward." Soren Kierkegaard

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