Looking for some help with device options

Looking for some help with device options

[Grantham, Ewan R.]

Am setting up a test machine for some writing I am doing, and the idea
is to do some RAID things without messing up my main machine and array
:-)

For the test machine I have three external firewire drives. The
"opportunity" here is that two of them are 200 Gigs, and the other one
is 80 Gigs.

My first thought is to break each drive up into multiple 40 Gig
partitions, and then RAID-5 all the partitions. Would I then be N-1
based on partition size (so 440 Gigs) or N-1 based on the largest device
(i.e. 280 Gigs)? Also, would setting up a RAID this way cause lousy
performance and possibly be less stable - or am I worrying too much?

Finally - any other "interesting" ideas for setting up the space? I
thought about mixing RAID types on the drives so that I would have a
RAID-5 of 80 Gig partitions, and then RAID-1 the remaining 120 Gig on
the two 200 Gig drives. But that strikes me as going particularly far
out on the limb.

Thanks for your help,
Ewan

Re: Looking for some help with device options

[Daniel Pittman]

On 26 May 2004, Ewan R. Grantham wrote:
> Am setting up a test machine for some writing I am doing, and the idea
> is to do some RAID things without messing up my main machine and array
>
> For the test machine I have three external firewire drives. The
> "opportunity" here is that two of them are 200 Gigs, and the other one
> is 80 Gigs.

[...]

> I thought about mixing RAID types on the drives so that I would have a
> RAID-5 of 80 Gig partitions, and then RAID-1 the remaining 120 Gig on
> the two 200 Gig drives. But that strikes me as going particularly far
> out on the limb.

Actually, that is the setup I would chose for this. It provides the
greatest degree of protection against drive failure possible for each
chunk of space, and provides the largest effective storage space for
each MD device.

The many 40GB partitions idea seems ... more complex, and less useful.

    Daniel
-- 
We live in a hallucination of our own devising.
        -- Alan Kay

Re: Looking for some help with device options

[Bernd Fischer]

Grantham, Ewan R. wrote:

> My first thought is to break each drive up into multiple 40 Gig
> partitions, and then RAID-5 all the partitions. Would I then be N-1
> based on partition size (so 440 Gigs) or N-1 based on the largest device
> (i.e. 280 Gigs)? Also, would setting up a RAID this way cause lousy
> performance and possibly be less stable - or am I worrying too much?

You would get 440 G, but at at price. Having more than one part of a 
RAID5 set on the same drive means that if that drive fails, the whole 
array does. Having more than one part of the array on every drive in 
effect triples the danger of data loss.


> Finally - any other "interesting" ideas for setting up the space? I
> thought about mixing RAID types on the drives so that I would have a
> RAID-5 of 80 Gig partitions, and then RAID-1 the remaining 120 Gig on
> the two 200 Gig drives. But that strikes me as going particularly far
> out on the limb.

Again, insufficient redundancy on the RAID-5. If you don't care about 
that, just use linear RAID or LVM to join partitions of arbitrary sizes. 
  Otherwise, you lose diskspace and cpu time for no benefit at all.

My setup would be a couple of RAID-1 or 5 devices across all three disks 
for the system and vital data, all the leftover bits joined up in a 
linear RAID for the not-so-vital stuff. It all depends on what the 
machine is suposed to do, though.


Bernd Fischer