Plutonians are teh s uck (krick) wrote,

SSD Partition Alignment

I just got some new toys. I picked up a pair of Intel X25-V 40GB SSD (Solid State Drives). SSD drives are basically the same type of flash memory that you use in your digital camera. The plan is to use them (in two different computers) to hold the operating system and applications. With an SSD, Windows launches in seconds and applications start up immediately. They use very little electricity and there are no moving parts so they generate no heat or noise. The drawback is that they're expensive (compared to conventional hard drives) and require special "handling". One of the things you need to do when you install one is called partition alignment. Windows Vista and Windows 7 align partitions correctly by default if you do a clean install on an un-partitioned drive. However XP (which I use) does not. I found this useful post from someone in the Intel forums...


To check alignment, run this command from a command line (Start, type "cmd" into the search box):
wmic partition get BlockSize, StartingOffset, Name, Index


This is what an unaligned partition looks like. Mine is a leftover from XP days, upgraded to Vista and then again to 7:
BlockSize  Index  Name                   StartingOffset
512        0      Disk #0, Partition #0  32256

That's a 63 sector offset. What were they thinking?


An aligned partition created by Vista / 7 will have an offset of 2048 blocks, which will look like this:
BlockSize  Index  Name                   StartingOffset
512        0      Disk #0, Partition #0  1048576


Running an SSD unaligned is throwing performance away. Your SSD "thinks" in 4k flash "pages". If you're mis-aligned, filesystem clusters span across flash pages, which means a very real performance hit.
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