Windows Disk Alignment Test

The Windows operating system writes data to disk in 64k chucks.  However, Windows Server 2000, 2003 and Windows XP all incorrectly begin writing data at the 63rd sector.  This means the first 1k of the chuck is written into one sector, and the remaining 63k in the next, and so on.  The consequence of this behavior means that for every read and write, two sectors must be accessed from disk instead of one.  This basically doubles your disk I/O. The additional I/O (especially if small) can impact system resources significantly.

Therefore, whenever a Windows host experiences a slowdown, you may want to check the disk alignment to determine whether the slowdown can be attributed to one/more unaligned disk partitions. This test enables you to perform such a check.

Target of the test : A Windows host

Agent deploying the test : An internal agent

Outputs of the test : One set of results for each physical disk partition on the Windows host being monitored

Configurable parameters for the test
  1. TEST PERIOD - How often should the test be executed
  2. Host - The host for which the test is to be configured
Measurements made by the test
Measurement Description Measurement Unit Interpretation

Disk partition alignment status:

Indicates whether this disk partition is aligned or not.


If the partition is unaligned, this test reports the value Partition is not aligned. For an aligned partition, this test reports the value Partition is aligned.

The numeric values that correspond to the above-mentioned measure values are described in the table below:

Measure Value Numeric Value

Partition is aligned


Partition is not aligned



By default, this measure reports one of the Measure Values listed in the table above. The graph of this measure however will represent the disk alignment status using the numeric equivalents - 100 or 0.

If a partition is found to be misaligned, you can use the detailed diagnosis of this test to figure out the caption, device ID, logical partition name, and block size of the faulty partition.