3TGKB-0056 : How do I optimise my disk partitioning for Exchange 2000/2003?

THE SCENARIO: Each track on a disk typically contains 64 sectors. When Windows creates a partition it uses the first 63 sectors (0 to 62) of the first track (0) for the Master Boot Record (MBR). Therefore, when you are formatting a partition you are actually starting from track 0, sector 63, which is the last sector of the first track. Each sector typically has a capacity of 512 bytes, so assuming that you choose Microsoft’s recommended cluster size of 4KB, then that means that each cluster contains 8 sectors. In theory, those 8 sectors would fit neatly into your 64 sectors on each track, but unfortunately, you are mis-aligned by one sector, which means the first sector and every eighth sector after that has spanned two tracks and cost you some hefty I/O. You can realise up to a 20% performance gain simply by aligning your disk formatting with the track boundaries.

ANSWER: To be certain of disk alignment, use Diskpart.exe, a disk partition tool. Diskpart.exe is a utility provided by Microsoft in the Windows Server 2003 Service Pack 1 Support Tools that can explicitly set the starting offset in the master boot record (MBR). By setting the starting offset, you can track alignment and improve disk performance. Exchange Server 2003 writes data in multiples of 4 KB I/O operations (4 KB for the databases and up to 32 KB for streaming files). Therefore, make sure that the starting offset is a multiple of 4 KB.

Before You Begin

Diskpart is a data destructive utility. When used against a disk, all data on the disk will be wiped out during the storage track boundary alignment process. Therefore, if the disk on which you will run Diskpart contains data, backup the disk before performing the following procedure.

Note: Diskpart can only be used with basic disks. Diskpart cannot be used with dynamic disks. Diskpart supersedes the functionality previously found in Diskpar.exe. Diskpar and Diskpart should only be used if the drive is translated as 64 sectors per track.

To align Exchange I/O with storage track boundaries using Diskpart.exe

1.	If the disk you are aligning is already blank (raw), proceed to Step 3. If the disk contains data, backup the disk before proceeding.
2.	Delete all partitions on the disk.
3.	Open a command prompt, and execute Diskpart.exe.
4.	At the Diskpart command prompt, type List Disk and press Enter. If the disk you want to align does not appear in the list make sure that it exists and is accessible using the Disk Management snap-in.
5.	At the Diskpart command prompt, type Select Disk X, where X is the number of the disk as shown in the output of the List Disk command. Diskpart should return a message that indicates that Disk X is the selected disk.
6.	At the Diskpart command prompt, type Create Partition Primary Align=X, where X is either 64 or 128, depending on the recommendation from your storage vendor. If your storage vendor does not have any specific recommendations, it is recommended that you use 64.
7.	At the Diskpart command prompt, type Assign Letter=<DriveLetter>. For example, to assign letter Z to the disk, type Assign Letter=Z.
8.	Once the drive letter is assigned, type exit to exit out of the Diskpart utility.
9.	Use the Disk Management snap-in or the Windows Format command to format the partition as an NTFS-formatted partition.

Help this helps! Another great article on this topic is at http://www.petri.co.il/exchange_disk_geometry.htm.

KB Keywords: Exchange optimise optimize disk diskpart diskpar SAN sector cluster track boundary

3TGKB-0056
Last Edited :	03-11-05
Revision :	1.0