Partition alignment largely a moot point now

To summarise. It is very important for recent disk performance that partitions are aligned on a 1MB/2048 sector boundary. This stops data from sitting astride blocks and killing disk performance. It is especially important with first generation SSDs, as they have poor write performance anyway, and will save your SSD from an early demise (flash memory has limited write cycles).

Windows Vista and above will use the 2048 sector alignment as will Ubuntu, so it isn’t necessary to worry about this issue any more, unless you are installing Windows XP. MAC OS X is the big loser in all of this as it doesn’t care about alignment beyond 4k which may or may not work well depending on the specific block size of your HD/SSD.

Partitions created on versions of Windows up to and including Windows Server 2003 by default are not aligned. Partition alignment must be explicitly performed.

By default, Ubuntu 10.04 LTS aligns partitions on disk to 1 MiB (1048576 bytes) boundaries. This ensures maximum performance on many modern disks, particularly solid state drives

Apple’s partitioning policy is as follows:

  • For all types of disks, we align each partition to a 4 KB boundary.

Where it does get messy is upgrading existing partitions. To summarise (again with the summarising what about some detail – Ed), you’ll need to copy existing partitions off using an imaging tool, such as dd, create new partitions and then copy the images back. In order to cope with the new partitions being slightly smaller than the old ones, because of the new alignment, you will need to decrease partition size before copy. All of this would be beyond the average user.

It should be possible to use GParted to simply resize the partitions to the correct sectors, but when I tried this with older versions it wouldn’t allow that granularity of control. Alternatively you could try parted from the cmd line but I have had several bad experiences resizing partitions with parted and can only recommend staying away from it.

References:-

Windows partition alignment best practices – http://msdn.microsoft.com/en-us/library/dd758814%28SQL.100%29.aspx

Partition alignment in Ubuntu 10.04 – https://wiki.ubuntu.com/LucidLynx/ReleaseNotes#Partition%20alignment%20changes%20may%20break%20some%20systems

Apple partitioning policy – http://developer.apple.com/library/mac/#technotes/tn2006/tn2166.html

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