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Performance Recommendations for Disk Alignment using Microsoft Windows

Technote (FAQ)


What are the recommended settings for best performance with SAN Volume Controller, Storwize V7000 and Storwize V7000 Unified when using Microsoft Windows operating systems and an application that generates a significant amount of I/O?


With SAN Volume Controller, Storwize V7000 and Storwize V7000 Unified Volumes, as with physical disks that maintain 64 sectors per track, the Microsoft Windows operating systems prior to Windows Server 2008 always creates a partition starting with the sixty-fourth sector by default. This results in the partition data layout being misaligned with the track boundaries of the volume. To ensure that these are both aligned on the older OS versions (Windows 2000 and 2003) you should use the diskpar.exe or diskpart.exe utility provided by Microsoft to define the starting location of the partition.

Windows Server 2008 automatically aligns new partitions at either a 64Kbyte or 1024Kbyte (1MB) offset (depending on the size of the partition), avoiding the need to manually align new partitions for track alignment.

The diskpar.exe command is part of the Microsoft Windows Server 2000 Resource Kit and is for use with Windows 2000 and Windows 2003. The diskpar.exe functionality was put into diskpart.exe with Windows Server 2003 Service Pack 1. Using either of these tools you can explicitly set the starting offset in the Master Boot Record (MBR).

The setting that you define depends on the allocation unit size of the formatted volume. An alignment of 64 (32Kbytes), or multiple of this value, will give the best performance with SVC, Storwize V7000 and Storwize V7000 Unified Volumes. If using an allocation unit of 64Kbytes or greater the alignment and allocation unit should be set to be the same. Doing so ensures track alignment and may improve the performance of applications like Exchange.

The allocation unit should be set to meet the preferences of the application - for applications that generate a transaction workload use a small allocation unit such as 4Kbytes, for sequential workloads use a larger allocation unit such as 64Kbytes.

Please follow the link below for more information on how to align I/O from Microsoft Exchange with storage track boundaries.

Please refer to the What's new in the IBM System Storage SAN Volume Controller Information Center for more information on SVC Terminology changes.

Related information

Microsoft TechNet: How to Align Exchange I/O

Cross reference information
Segment Product Component Platform Version Edition
Storage Virtualization SAN Volume Controller 6.4 SAN Volume Controller 4.3, 5.1, 6.1, 6.2, 6.3, 6.4
Disk Storage Systems IBM Storwize V7000 (2076) Not Applicable IBM Storwize V7000 6.1, 6.2, 6.3, 6.4
Disk Storage Systems IBM Storwize V7000 Unified (2073) Not Applicable Platform Independent 1.3

Document information

More support for: IBM Storwize V7000 (2076)

Version: Version Independent

Operating system(s): Platform Independent

Reference #: S1003291

Modified date: 06 November 2009