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2010/10/06 / Oleg Soroka

Align VMDK or LUN to the 64k offset

When deploying vmware virtual machine on top of VMFS on top of a NetApp SAN, you need to make sure to align it properly otherwise you will end up with performance issues. File system misalignment is a known issue when virtualizing. Also, when deploying LUNs from a NetApp appliance, you need to make sure no to reformat the LUN, or you will lose the alignment, just create a filesystem on top of the LUN.

NetApp provides a great technical paper about this at: http://media.netapp.com/documents/tr-3747.pdf

In this post Iwill show you how to align an empty vmdk disk/LUN using the open source utility GParted. This is for new vmdk disks/LUNs, dont do it on disk that contain data as you will lose it. This is for Golden Templates that you want aligned, so subsequent virtual machines will inherit the right alignment, or for servers that need a NetApp LUN attached.

The resulting partition works for Linux and Windows, just create a filesystem on top of it.

You can find GParted at: http://sourceforge.net/projects/gparted/files/

1. Boot the VM from the GParted CD/Iso. Click on the terminal icon to open a terminal:

2. Check the partition Starting Offsets, in this case I have 3 disks 2 are already aligned to the 64k offset, I will align the new disk as well.

3. Create an aligned partition on the drive using fdisk

gparted# fdisk /dev/sdc

Below is a screenshot of the answers to fdisk, the important option is to select to start the offset at 64k, as indicated.

4. Now check again and the partition should be aligned

[root@server ~]# fdisk -lu

Disk /dev/sda: 209 MB, 209715200 bytes
64 heads, 32 sectors/track, 200 cylinders, total 409600 sectors
Units = sectors of 1 * 512 = 512 bytes

Device Boot Start End Blocks Id System
/dev/sda1 * 64 409599 204768 83 Linux

Disk /dev/sdb: 77.3 GB, 77309411328 bytes
255 heads, 63 sectors/track, 9399 cylinders, total 150994944 sectors
Units = sectors of 1 * 512 = 512 bytes

Device Boot Start End Blocks Id System
/dev/sdb1 * 64 41943039 20971488 8e Linux LVM

Disk /dev/sdc: 107.3 GB, 107374182400 bytes
255 heads, 63 sectors/track, 13054 cylinders, total 209715200 sectors
Units = sectors of 1 * 512 = 512 bytes

Device Boot Start End Blocks Id System
/dev/sdc1 64 209715199 104857568 83 Linux

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