More fun with Linux RAID and LVM

In an earlier post, I performed a test RAID5 + LVM set up using files instead of disks. Now I'm going to fail a 'disk', replace it in the array, and then expand the LVM logical volume to include a second RAID5 array.

In this example, I'll replace out /dev/loop2 as the faulty member. So, mark it as faulty, and remove it from the array. I'll also delete the loopback device.

mdadm /dev/md0 --fail /dev/loop2
mdadm /dev/md0 --remove /dev/loop2
rm /var/tmp/hdc.img
losetup -d /dev/loop2

Next, create a new disk, and add it to the array:

dd if=/dev/zero of=/var/tmp/hdc.img bs=1024 count=1048576
losetup /dev/loop2 /var/tmp/hdc.img 
fdisk /dev/loop2
partprobe
mdadm /dev/md0 --add /dev/loop2

And the rebuild will begin. Check its progress with:

mdadm --detail /dev/md0

Now follow the steps in my previous post to build a second RAID5 array and call it md1; we'll be using using it to extend our original LVM volume group.

[root@canard ~]# vgscan
  Reading all physical volumes.  This may take a while...
  Found volume group "vg_media" using metadata type lvm2

pvcreate /dev/md1
vgextend vg_media /dev/md1

Find the total number of extents you have available, resize the LV to that new number and grow the EXT3 filesystem for the free space on your device:

[root@canard ~]# vgdisplay vg_media | grep "Total PE"
  Total PE              1010

So we'll extend to 1010 physical extents.

lvextend -l 1010 /dev/mapper/vg_media-lv_media 
resize2fs /dev/mapper/vg_media-lv_media

If all went according to plan, you should now have a ~4GB LV with no remounting required.

[root@canard ~]# lvdisplay /dev/vg_media/lv_media
  --- Logical volume ---
  LV Name                /dev/vg_media/lv_media
  VG Name                vg_media
  LV UUID                iS01Vt-Hyo7-GIiA-Sxlu-rc5J-bX5g-Trd9Ln
  LV Write Access        read/write
  LV Status              available
  # open                 1
  LV Size                3.95 GB
  Current LE             1010
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0