On Tue, Apr 09, 2002 at 11:18:00PM +0200, Anders Widman wrote:
> I have a problem which I want to solve as efficiently as possible.
> The problem is that I have 13 drives os various sizes (30-120GB) which
> I want to combine into one (or a few) logical volumes with redundancy
> if one drive would fail.
> How would the smartest layout be? I was thinking about multiple
> partiontions and then combine them into several RAID 5 chains, and
> then use LVM to manage the logical volumes.
The problem (off the top of my head) is that (1) this will give
utter crap performance, and (2) If you're not *really* careful with
your layout you could wind up losing a lot of data in a crash and
(3) even if you don't loose data in a crash, a single drive fault
will still drag performance into the toilet.
> There is an expamle of my ideas at http://www.tnonline.net/raid-lvm.png
> As you can see there are 8 chains and about 50 GB unallocated data in
> this example. Can I minimize the loss even better?
Using MD to make some meta-devices on the raw drive do:
Stripe:
2x60 = 120
2x60 = 120
2x60 = 120
Raw:
120x1=120
Then layer these devices to become your initial RAID5 volume.
That leaves 2x75, 2x80, 1x30, and 1x40:
Linear mode the 30 and 40 to get 70, raid5 across these to get:
80
80
75
75
70 (30+40).
This loses you about 30 gig. (10+10+5+5). If you really wanted you
could recover that by working off partitions, but IMO it's just not
worth it.
--
Share and Enjoy.
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