20 Oct 09 Setting up an LVM filesystem

Setting up an LVM filesystem is quite easy assuming you have the right tools installed and a recent kernel. LVM has a lot of advantages, most notably the ability to take snapshots of the current filesystem – this is why LVM is often used in live database environments.

Assuming a Debian Lenny machine, get the relevant packages. Some may already be installed:  apt-get install lvm2 dmsetup mdadm

In this example, we will assuming that /dev/sda is your boot drive, and that you want to leave it out of your LVM array, but include /dev/sdb and /dev/sdc. Both /dev/sdb and /dev/sdc should be of equal sizes.

Firstly, using fdisk, remove any existing partitions with ‘d’, on /dev/sdb and /dev/sdc, and create one new partition to span the drive. Change the partition type to ’8e’ which is the LVM type.

Now prepare your physical disk for LVM with the ‘pvcreate’ tool:

pvcreate /dev/sdb1 /dev/sdc1

Note that you can reverse this with pvremove. You can also use pvdisplay now to display information on all physical volumes.

Oh – you do realie that you can use /dev/mdX just as easily to create LVM on your RAID devices?

Now, we need to create a ‘volume group’: vgcreate myvg /dev/sdb1 /dev/sdc1

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Tags: dd, ext3, kernel, Linux, lvcreate, lvdisplay, lvm, lvremove, mkfs, mount, pvcreate, pvdisplay, pvremove, resize, tar, vgcreate, vgdisplay, vgremove, xen

26 Sep 09 Shrinking/Resizing ext3 Partitions

Shrinking or expanding an ext3 partition is easy but is not without it’s risks. Before starting, you NEED to take a backup of your data. There’s a strong possibility that it will all disappear and your filesystem will become permenantly broken, as with any disk or filesystem procedure.

Please note:

1. The steps below are the RAW STEPS required to resize your partition. This is a potentially dangerous procedure that could easily destroy/ruin/damage your partition, data, filesystem or other partitions on the same disk.
2. DO NOT perform these steps on a live/production machine
3. DO NOT perform these steps unless you have a full backup of your data/disk
4. These steps are really for theoretical purposes only. They should work just fine, but tools such as gparted will do this for you.

ns3:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1             9.4G  6.8G  2.2G  77% /
tmpfs                 443M     0  443M   0% /lib/init/rw
udev                   10M   92K   10M   1% /dev
tmpfs                 443M     0  443M   0% /dev/shm
/dev/sdb1              20G  9.8G  9.0G  52% /email

In my example, I’m going to resize /dev/sdb1 which is my /email partition. /dev/sdb1 is a partition residing on device /dev/sdb

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Tags: df, ext3, fdisk, fsck, resize, resize2fs, tune2fs

08 Mar 09 How to create a simple disk image formatted to ext3

We want a 48MB image, formatted to ext3

ns3:/tmp# dd if=/dev/zero of=./disk.img bs=1MiB count=48
48+0 records in
48+0 records out
50331648 bytes (50 MB) copied, 0.301372 s, 167 MB/s
ns3:/tmp# mkfs.ext3 ./disk.img
mke2fs 1.41.3 (12-Oct-2008)
./disk.img is not a block special device.
Proceed anyway? (y,n) y

ns3:/tmp# mkdir disk

ns3:/tmp# mount -oloop ./disk.img ./disk
ns3:/tmp# df -h ./disk
Filesystem            Size  Used Avail Use% Mounted on
/tmp/disk.img          47M  4.8M   40M  11% /tmp/disk

That’s it – now we can copy our content to ./disk before unmounting it, then use dd to write it to our target medium (such as a CF card or similar)

ns3:/tmp# umount ./disk

Tags: CF, df, disk image, ext3, loop, mkfs.ext3, mount, umount