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How to Align Exchange I/O with Storage Track Boundaries

Applies to: Exchange Server 2007 SP3, Exchange Server 2007 SP2, Exchange Server 2007 SP1, Exchange Server 2007

Topic Last Modified: 2007-01-22

This topic explains how to use the Diskpart tool to align Exchange I/O with storage track boundaries. With a physical disk that maintains 64 sectors per track, Microsoft Windows always creates the partition starting at the sixty-forth sector, therefore misaligning it with the underlying physical disk. To be certain of disk alignment, use Diskpart.exe, a disk partition tool. Diskpart.exe is a tool 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). Setting the starting offset correctly will align Exchange I/O with storage track boundaries and improve disk performance. Microsoft Exchange Server 2007 writes data in multiples of 8-kilobyte (KB) I/O operations, and I/O operation to a database can be from 8 KB to 1 megabyte (MB). Therefore, make sure that the starting offset is a multiple of 8 KB. Failure to do so may cause a single I/O operation spanning two tracks, causing performance degradation.

Before You Begin

Diskpart is a data-destructive tool. When used against a disk, all data on the disk will be deleted during the storage track boundary alignment process. Therefore, if the disk on which you will run Diskpart contains data, back up 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.

Important:
Many vendors now have specific tools and guidance for sector aligning their storage platform. You should check with your storage vendor before performing a sector alignment change with Diskpart. If your storage vendor does not have tools for this task or specific guidance for sector aligning their storage platform, we recommend that you use Diskpart to properly align your storage volumes.

To perform this procedure, the account you use must be delegated membership in the local Administrators group.

For more information about permissions, delegating roles, and the rights that are required to administer Exchange Server 2007, see Permission Considerations.

Procedure

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

If the disk you are aligning is already blank (raw), proceed to Step 3. If the disk contains data, back up the disk before proceeding.
Delete all partitions on the disk.
Open a Command Prompt window, and run Diskpart.exe.
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.
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.
At the Diskpart command prompt, type Create Partition Primary Align=X, where X is the value recommended by your storage vendor. If your storage vendor does not have any specific recommendations, we recommend that you use 64.
At the Diskpart command prompt, type Assign Letter=<DriveLetter>.
After the drive letter is assigned, type exit to exit the Diskpart tool.
Use the Disk Management snap-in or the Format command to format the partition as an NTFS-formatted partition.

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FAQ

Disk Alignment with Exchange 2007

Its true. Older versions of Windows would align to sector 63 (offset 32,256b) by default. Some SAN vendors would recommend aligning to sector 64 (offset 32,256b) to make best use of SAN side cache.

This isn't really necessary in Windows 2008 and 2008 R2 as we now align to sector 2048 (offset 1,048,576), which would properly align the partition boundaries.

History

3/23/2011
Robert Mitchell [MSFT]

Missing some critical concepts?

Modern disk drive controllers completely hide the physical CHS layout and the storage driver never sees the physical disk layout. All modern high capacity disk drives use a technique called Zone Bit Recording that increases the sector density from the innermost to the outermost track/cylinder to maximize area recording density. However this is irrelevant since all modern disk drives are now accessed using Logical Block Addressing (LBA) scheme where the sectors are simply addressed linearly from 0 to some maximum value and disk partition boundaries are defined by the start and end LBA address numbers. Thus this article is missing a critical point if it rationalizes physical disk optimization using the concept of physical disk parameters which are not exposed to the storage driver at all. This is especially true of RAID and SAN storage systems where storage device access undergoes multiple layers of processing before any physical disk is accessed. I think the optimization that occurs using the diskpart.exe utility setting the Align value to 64 forces the partition to be defined in integer multiples of 64 kilobytes and also that disk drive controllers internally buffer and process data in 64 kB blocks. Formatting the NTFS partition in 64kB clusters matches cluster size with hardware processing block size but may not be optimal use of disk capacity owing to the mis-match between mean file sizes and cluster sizes but this is not a factor when creating Exchange and SQL database storage volumes which manage their own data structures in pages and extents. Anthony Maw, Vancouver, Canada, anthony@maw.bc.ca

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