[ILUG] Why RAID

[Rick Moen]

Quoting John P. Looney (valen at tuatha.org):

> The next level up are the crappy pretend
> hardware RAID. Highpoint and Promise come to mind here. This can be a
> world of pain. Promise drivers are poor, and the machine still falls over
> when a disk dies - it has to be replaced with a new one before it'll work.

Adding insult to injury:  Suppose your Highpoint/Promise card itself
commits seppuku.  That might motivate you to finally do the sensible
thing and migrate to Linux "md" driver software RAID -- but, sorry, you
lose:  To regain access to the data on your RAID set, you need to buy
another of the same (or very similar) Highpoint or Promise card _first_,
before you can ransom back your data.

And, of course, if for some reason those cards are no longer available,
you have a lovely opportunity to find out how good your tape-restore
system is.

> You can then get a proper hardware RAID card.

I'm curious what people regard as proper hardware RAID cards, these
days.  I long ago became disenchanted with Mylex cards:  They're not
only a king's ransom to start with, but also tend to suffer severe
congestion problems under load, on Linux.  I'm tempted to go dig up the
ashes of my friend Leonard Zubkoff (who wrote the drivers) and kick him
for that.

On the ATA I'm-feeling-lucky-and-don't-mind-high-defect-rates-and-low-MTBF
side of things, there's Adaptec AAR 24x0, LSI Logic (formerly AMI) MegaRAID, 
and 3Ware Escalade 8xxx.  The Adaptec has an optional battery-backed
cache daughtercard, which disables the attached drives' caches,
eliminating the most troubling ATA catastrophic-data-failure mode.
With suitable enclosures, you can even get hotswap / hot spare, though 
drive-failure notification is an interesting question.

How are people doing with those?

On the SCSI side, I guess you have those same suspects less 3Ware, and
also the aforementioend Mylex (ex-Buslogic, ex-Bustek).  I think those
might be reasonable.

> Though this can also be painful - we learned the hardway that if you put a
> certain brand of IBM disk into an Intel SR2300 without upgrading the
> disk's firmware, you can corrupt your RAID array.

Indeed, qualification of drives for RAID controllers at
$FORMER_DOTCOM_LINUX_FIRM was an ongoing nightmare; sometimes, changes
of drive firmware would make the whole house of cards collapse.  Linux
"md" software RAID looked better, the more I encountered such things.

-- 
Cheers,             "Don't use Outlook.  Outlook is really just a security
Rick Moen            hole with a small e-mail client attached to it."
rick at linuxmafia.com                        -- Brian Trosko in r.a.sf.w.r-j