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What is partition alignment and how to align partition

Partition alignment

Refers of the starting location of the logical block (LBA) or sector partition created by the operating system.


Condition where the start of the logical sector location used by the host file system and/or software application does not match the start location of the physical sector on an Advanced Format HDD. Misalignment may result in a degradation of the performance capabilities of the AF HDD-installed system.

Misalignment issue:

Disk performance may be slower than expected when you use multiple disks in Microsoft Windows Server 2003, in Microsoft Windows XP, and in Microsoft Windows 2000. For example, performance may slow when you use a hardware-based redundant array of independent disks (RAID) or a software-based RAID.

This issue may occur if the starting location of the partition is not aligned with a stripe unit boundary in the disk partition that is created on the RAID.

Why realign partition

A volume cluster may be created over a stripe unit boundary instead of next to the stripe unit boundary. This is because Windows uses a factor of 512 bytes to create volume clusters. This behavior causes a misaligned partition. Two disk groups are accessed when a single volume cluster is updated on a misaligned partition.

Windows creates partitions that are based on a predefined number of sectors. The starting location for a disk partition in Windows Server 2003 is either the 32nd or the 64th sector, depending on the information that is presented to the operating system by the mass storage controller.

Partition alignment issue on SSD

If you've already migrated to an SSD, you might not have realized that you're sacrificing performance with misaligned partitions. A regular hard drive usually starts its first partition after 63 empty blocks, while SSDs require 64 blocks of data for optimal performance. This means that sometimes, if your SSD was formatted by something other than Windows' installer, it can be aligned incorrectly and will transfer data much slower than intended.

How to identify if your partitions are aligned correctly

To see if your partitions are aligned correctly, hit the Start menu and enter "Msinfo32" and then go to Components > Storage > Disks. Look for your SSD on the list and find the "Partition Starting Offset" item. If this number is divisible by 4096 (that is, if dividing it by 4096 equals a whole number and not a decimal), your partition is correctly aligned. If not, you need to realign it.

How to align partitions?

By aligning partition, you can improve the data read and write speed of the disk.

Step 1, Download, install and launch partition assistant, right click the partition you want to align and then select "Advanced" > "Align Partition".

Align partition

Step 2, in the pop up window, set partition alignment, for SSD, 1024 is recommended.

Realign partition

Click OK and back to main window, press "Apply" button on top left to proceed, done.

If the partition has been aligned, you'll receive a message as below if you realign the partition.

Realign complete

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