Raid 5 (was: Mounting of Linux volumes)

[Michael Torrie]

On Thu, 2005-12-01 at 18:46 -0700, Ross Werner wrote:
> On Thu, 1 Dec 2005, Jeff Schroeder wrote:
> > Bang for the buck.  I'm using 300GB+ drives, and having to buy 33% more
> > drives for the redundancy (is my math right?) can get expensive across
> > many servers.
> 
> What's your process for when a drive fails on your software RAID 5 
> machines? Have you always been able to boot with one drive gone? Or do you 
> have some sort of boot CD with software RAID configured properly on it? I 
> have only tried out RAID 5 once, on a server that ate hard drives for 
> lunch, and I was never able to successfully boot after a drive bit the 
> dust, and using software RAID whenever a drive failed the machine would 
> lock up completely.

Sure.  On hardware RAID, there's no problems booting off a degraded
RAID.  If you only have software RAID-5, linux can't boot off that
anyway, so there's no problem.  Just create a boot partition on either a
separate drive, or a separate partition.  The problem with the latter is
if the disk that failed had you boot partition, you are out of luck.  A
way around that would be to clone the boot partition onto every disk I
suppose.

In any event, software RAID-5 does have significant issues to plan for
and I would not recommend using it in a situation where hardware RAID-5
is clearly the better way to go.  Even for home use, for $200 you can
pick up a pretty decent SATA RAID controller.

The way  I look at it, for my persona use, my home directory is most
important.  So if I'm going to use Software RAID-5 to get lots of
storage, I'll put my home directory there, along with my general storage
area.  Then I run a separate root disk and mount it in.  The Linux
install itself is expendable.  my data isn't.

Michael


> 
>  	~ Ross
> 
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-- 
Michael Torrie <torriem at chem.byu.edu>