Answer on mirror problem with /usr

Answer on mirror problem with /usr

Post by Marcel La » Thu, 24 May 2001 16:59:18

Did you try synclvodm ?

1. Smoke and Mirrors: mirrored concat / concat mirrors

Hi all - I have a JBOD with a bunch of disks, and need to create a
~200gb slice on this using LVM on Sol 9. I've allocated 2 disks to a hot
spare pool already. This leaves me with 6 new disks in order to create
my ~200gb slice. They're all on the same controller, nice (not my choice).

I'm thinking of ways to do this.

Example 1:

mirror d4, made up of a concat of disks 0,1,2 (d14) and a concat of
disks 3,4,5 (d24)


             d14            d24
           0  1  2         3 4 5

If I lose a disk on one side the spare should kick in, but if I lose
another disk on the other side whilst this is syncing, I've lost my
data. I could lose up to three disks (on one side only) and still serve
up data.

Example 2:

mirror d4, made up of a concat of mirrors d14 (disks 0,1), d24 (disks
2,3) d34 (disks 4,5)


                   d14 0 1
                   d24 2 3
                   d34 4 5

Here I can lose up to 3 disks (in different mirrors) but if I lose 2
disks in the same mirror I'm knackered. However if I lose one disk I'm
only syncing up 72gb of data as opposed to ~200gb in example 1.

Is example 2 any better than example 1 for resiliency? Will LVM even
allow me to do this? If anyone has any suggestions I'd be most
appreciative. Resiliency is more important than outright speed, and read
speed is more important than write speed.

Maybe I should stick with example 1.

Or is it too early on Monday and I haven't had enough coffee yet :) Damn
long weekends and no sleep.



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