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I'm buying a new SSD. One of the specs I'm comparing is 4k Random Write (Aligned): 50,000 IOPS and 4k Random Write (Aligned): 10,000 IOPS.

What does this spec mean?

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up vote 6 down vote accepted

Random write as in it writes data to random locations all over the drive (this is similar to what average usage of a machine does - writes a small log file here, a small cookie there, etc), 4K as in the size of the files (aka fairly small). Aligned here refers to the internal logic - 4K tends to be the page size on these things, so you're not trying to make two writes at once if they're properly aligned with the boundaries (which would obviously hurt speed).

IOPS are Input/Outputs per Second, more obviously being better. Note though that not all drives are created equal. I recommend you read some reviews before you pull the trigger - AnandTech is great for advice on SSDs.

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Thanks for the Anand tip. This really blew my mind: – Soup Dec 9 '10 at 19:59
I actually had that article in mind but I was on my way out the door so I didn't have time to dig it out, haha! Hope you've learned something. ;) – Shinrai Dec 9 '10 at 20:39

IOPS is a common benchmarking indicator, representing the number of mixed read/write operations which can be handled in one second by the the storage device.

The "Aligned" mention is present because most SSD works with 4k-sized sectors, so read/write operation to adresses aligned to this size have better performances that random-located ones (which would need to read and/or write across multiple blocks)

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