Re: Is shrinking raid5 possible?

[Thomas Arthur Oehser <tom@toms.net>]

> > 2) One wants to do something else with some of the space, although for
> > a RAID5 I don't quite see the point - you'd end up with n small
> > partitions. Shrinking a 2-way mirror or stripe this way sounds far
> > more useful.

Oooh, what would I want to do with "n small partitions"?  I know!  Raid!

Scenario:

existing:
sda1 sdb1 sdc1 254M + 254M + 254M = 254M raid-1 /boot
sda2 sdb2 sbc2 2G + 2G + 2G = 6G raid-0 swap
sda3 sdb3 sdc3 1.5T + 1.5T + 15.T = 3T raid-5 /

desired:
sda1 sdb1 sdc1 254M + 254M + 254M = 254M raid-1 /dev/md1 /boot
sda2 sdb2 sbc2 2G + 2G + 2G = 6G raid-0 swap /dev/md2
sda3 sdb3 sdc3 1.4T + 1.4T + 1.4T = 2.8T raid-5 /dev/md3 /
sda4 sdb4 sdc4 100G + 100G + 100G = 200G raid-5 /dev/md4 / <= alt for Koala

Since /dev/md3 is still only 70% full, I thought I could do something like:

 - resize2fs /dev/md3 <smaller>
 - mdadm -G -z <smaller> /dev/md3
 - fdisk /dev/sd[a-c]3 <smaller>

It _almost_ works fine... but... the mdadm -G keeps the (0.90) superblock
at the _end_ of the _device_ ... which hasn't been resized yet ...

How do I put the superblock back after fdisk, or make -G move or recreate?

-Tom