Best allocation unit size for ReadyBoost (Win7)
Sunday, December 4, 2011 10:03:33 AM
Testing was done using CrystalDiskMark 3, both 4K and 512K tests which in case of ReadyBoost matter the most. I was testing random read and write for 4K, 512K, 1M and 32M allocation units using exFAT.
The winner? Well, even though random read figures were changing a bit, they were basically a double digit figures on both SDHC cards. Not really important if you ask me. However, random write was severely affected and that was shown in triple digit numbers. Only 512K random write was affected where 4K random write remained unchanged.
Lets crumble the info down a bit:
Best 4K read: 32M allocation unit size
Best 512K read: 32M allocation unit size
Best 4K write: doesn't matter, anything from 4K to 32M
Best 512K write: 512K allocation unit size
So, if you want to squeeze absolutelly everything out of the ReadyBoost device, use 32M allocation unit size. ReadyBoost's primary task is to assist HDD with very fast random read. However, if random writes are slow, it might take longer to write cache data to the SDHC card. I can't really tell how this might reflect in real world situations but the best bet would be to test both, 512K and 32M and pick one of these that might work the best for you. If you just don't want to bother, use 32M allocation unit size as the random read speed is what most will be looking for.