Re: RAID
On Wed, Jul 18, 2001 at 09:51:36PM +0530, shyamk@eth.net wrote:
> Can somebody please tell me all about RAID .
I could, but it's a lot easier to just tell you to find a copy of the
Software-RAID-HOWTO.
> If I set up RAID autodetect on say /dev/hda4 ,
> does it destroy data any where ?
For starters, you can't do RAID on a single partition. While you could
create a RAID volume from multiple partitions on a single disk, the
results would be worse than just not using RAID - both in performance
and reliability. Since you asked about hda rather than sda, I'll also
throw in that doing RAID between two drives on the same IDE controller
(e.g., hda/hdb or hdc/hdd) will also kill performance. If you're going
to do IDE RAID, don't attach more than one hard drive per IDE controller.
Now, having gotten all that out of the way, I'll assume that you want
to set up a RAID using /dev/hda4 and /dev/hdc4. Setting up the RAID
will combine these two physical partitions into a single virtual
device, /dev/md0. Once this is done, hda4 and hdc4 are, for all
practical purposes, gone. When md0 is formatted, all their data will
be overwritten, just like any other time you format a partition. Once
md0 is created, forget that hda4 and hdc4 ever existed, because you
will corrupt md0 if you modify either one directly.
If md0 already exists, but isn't autodetected, I suspect that you should
be able to turn autodetect on without causing any problems. It would be
a lot safer (and just make more sense) to make it autodetected from the
start. I know that I've changed partition types to enable autodetect on
already-running RAIDs, but that's no guarantee that yours won't self-
destruct.
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