sata raid

[Peter Whittaker]

On Sat, 2007-28-04 at 09:56 -0400, Chris Patten wrote:
> I have a sata raid card and 2x500 gig sata drives, I want to disk
> mirror or raid0/1.  The raid is handled in the hardware of the card,
> not software.  It worked well under windows, windows showed 1x500 gig
> drive.  Now under ubuntu it shows 2x500 gig drives.  Why?  And what do
> I need to change? 

Chris, in all likelihood, RAID was not actually handled in the card
under Windows, but was faked out by a driver that shipped with Windows.
In other words, Windows "saw" a RAID device, because it had been *told*
to see one.

There are at least two reasons for believing this: 1) "real" hardware
RAID controllers are *very* expensive (not really consumer itema), and
2) if the card did the RAID, Linux - Ubuntu included - would see a
single drive, not two.

Real hardware RAID does NOT require software/OS drivers.

All is not lost, however! Setting up RAID under Linux is very easy,
thanks to the various utilities that come with the OS. Please refer to
the "super simple md recipe" on [1]; if you need assistance, contact me
directly, either by email or by phone [2].

NOTE! The "recipe" assumes there is no data on the array, that is, that
both disks are fresh and clean and ready to be formatted. If you have
data on your Windows RAID array, and you want to preserve it under
Linux, then you will either need to back the data up, performing the
recipe (tailored to your needs), then restore the data to the array, or
make the array available to your Linux boxes via a Windows file server.

Neither alternative is all that attactive, so if someone has a Buzz
Lightyear answer [3], post it here!

The recipe I added to [1] is easy to tailor to your needs, if you know a
little bit about Linux file systems.

In "the recipe", /dev/hdc and /dev/hdd are what Linux sees the two
identical drives as (the two 500Giggers, in your case), mke2fs creates
ext2 filesystems on each drive, mdadm creates the RAID pair ("-l 1"
means RAID Level 1), and the cat command adds the entry for the new disk
to /etc/fstab. (Why ext2 instead of ext3? I figured with RAID the
journalling was less important, and that the performance may be better
with ext2. I could easily be wrong on both points, I'd appreciate
comments... ...I can always reformat my array). 

The man pages are quite readable, please do plunge in if you need more
information.

Or call!

pww

[1] https://wiki.ubuntu.com/Raid

[2] 613 294 6916

[3] In Toy Story 2, Mr Potato Head offers Woody a choice of deaths: By
monkeys or by shark. Woody chooses Buzz Lightyear. "Buzz Lightyear?
That's a not a choice", screams Potato Head. Presto, Buzz appears and
saves the day. I *always* choose Buzz Lightyear. Just like Kirk did on
the Kobayashi Maru [4]. It just sometimes takes three tries and little
hacking to get there.

[4] http://en.wikipedia.org/wiki/Kobayashi_Maru


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