[sclug] RAID-1 on asymmetric disks?

Alex Butcher lug at assursys.co.uk
Sat Mar 7 21:12:47 UTC 2009

On Sat, 7 Mar 2009, Will Dickson wrote:

> Hi all,
> I've recently acquired a spare PC: nforce3 chipset and 2 PATA disks, one is 
> 120GB and the other about 200GB. It seems to be fine, but given the amount of 
> dreck I hoovered out of it before turning it back on, I'm slightly concerned 
> about the life expectancy of the disks.
> This gave me the following idea: use 60GB of the larger disk for a root 
> filesystem etc, and gang one partition of the larger disk, plus the whole of 
> the smaller disk, into a 120GB RAID-1 software mirror to use for data.
> - Is this idea completely daft, or does it sound feasible?

I doubt you'll encounter any problems. I do md RAID between partions "all the
time"; I even tend to have a RAID0 paid and a RAID1 pair - the former for
'disposable' parts of the hierarchy, like /tmp

> - If feasible, what would be the best software mechanism to go with - LVM, 
> md, something else?

LVM isn't RAID, though it does allow one to to agglomerate different bits of
disc into a single block device, and divvy it up dynamically.

md is the way to go, and you might want to put LVM on top in order to
dynamically reassign space between logical volumes (= partitions,

> I'm running Ubuntu 8.10 on my main machine, so I was looking at going with 
> that on the new box as well. Alternatively, I wouldn't mind giving CentOS or 
> Fedora a go - broaden the horizons and all that.
> Any comments, either on the RAID or the distro choice, gratefully received.

Not aware of any problems with Ubuntu, but I happen to use Fedora and

> Will.


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