lvm

On running daily lvm snapshot backups via vzdump on OpenVZ servers, I noticed the below Kernel errors in logwatch reports.

This would show up on busy servers only, probably caused due to lvm snapshot running out of space.

I edited "/usr/bin/vzdump" and increased the size from 500m to 1000m which seems to have resolved the issue for now.

I have outlined below the steps taken to move from a normal single disk system and convert to a raid1 using an additional drive:

Note: /boot cannot be on lvm nor any other raids other than raid1 partition.

Don't forget to make the essential backups prior.

Convert / to raid/lvm

1. fdisk /dev/sdb and make clone of sda (convert partition type to "Linux raid autodetect")
   
2. add /dev/sdb1 -- /boot - 13 blocks (100Mb) - type raid
   
3. add /dev/sdb2 -- rest - type raid
   
4. Create raid partitions:
   
   partprobe
mdadm -C /dev/md0 --auto=yes -l 1 -n 2 missing /dev/sdb1
mdadm -C /dev/md1 --auto=yes -l 1 -n 2 missing /dev/sdb2

5. Create logical volume and copy / partition and /dev files over:
   
   pvcreate /dev/md1
vgcreate vg0 /dev/md1
lvcreate -L 4G -n lv0 vg0
mke2fs -j /dev/vg0/lv0
mkdir /mnt/lv0
mount /dev/vg0/lv0 /mnt/lv0
find / -xdev | cpio -pvmd /mnt/lv0
cp -aux /dev /mnt/lv0

6. Edit /mnt/lv0/etc/fstab to reflect the new root
   
   /dev/vg0/lv0            /                       ext3    defaults        1 1

7. Chroot to new filesystem an create initrd with raid and lvm support
   
   chroot /mnt/lv0
mount -t proc /proc /proc
mount -t sysfs /sys /sys
vgscan
vgchange -ay
mkinitrd -v /boot/initrd-2.6.18-92.1.6.el5.lvm.img 2.6.18-92.1.6.el5

8. Edit grub.conf to point to new root /dev/vg0/lv0
   
9. reboot

Convert /boot to raid1

I've had to reduce the logical volume that was alloted for mysql data from 8GB to 4GB, which was a breeze with e2fsadm available for lvm1 on RHEL-3 .

Stop the running serivces using the volume:

e2fsadm will reduce the filesystem and then the logical volume.

Check with df, which should now show the new volume size:

Start the running serivces using the volume:

Note: e2fsadm is not available in lvm2 and will need to reduce in two steps:

1. Reduce the filesystem residing on the logical volume.
2. Reduce the logical volume.

I converted root filesystem to lvm since the root partition was huge and I needed more flexibility in managing the partitions. Besides, lvm would also enable for easy backups with lvm snapshots.

I had a sizable swap partition of 2GB which I used to transfer my root files to and rebooted to it, prior to the conversion.

Please know what you are doing prior and make sure to create backups.

Extend partition by 1Gb.

• resize2fs has replaced ext2online in FC6.
  
• need to unmount volume prior to doing resize2fs.

I was only using a part of my external usb hard drive to keep backups and needed to extend the partition to accomodate the ever-growing backup files.

There are quite some ways to do this which can be referenced at FedoraNews.org and TLDP.org .

Below is a quick command line reference if you are familiar with the process already.

1. I added an additional 10GB of space:
   

   # lvextend -L+10G /dev/vg00/lvol0
   

2. Unmount the drive:

   # umount /mnt/usbdisk
   

3. Check the logical volume:

   # e2fsck -f /dev/vg00/lvol0
   

4. Increase the file system size to match.

   # resize2fs -pf /dev/vg00/lvol0
   

5. Remount:

   # mount /mnt/usbdisk