I just read this very interesting article about the new 4096-byte sector hard disks, like the new Western Digital Caviar Green drives, and the impact a partition misalignment might have on the drive’s write performance.

The problem most likely to hit you with one of these drives is very slow write performance. This is caused by improper logical-to-physical sector alignment. OS’s like Linux use 4K blocks (or multiples of 4K) to store data, which matches well with the physical sector. However, nothing restricts you from creating a partition that starts on an odd-numbered 512-byte logical sector. This misalignment causes a performance hit since the drive has to read and rewrite the 4K sectors with whatever 512-byte slices changed.

The article author continues with a test he performed on two identical WD Green drives containing one partition. On the first drive he used fdisk defaults for the partition boundaries, while on the second drive he manually aligned the partition. The results show that a misaligned drive can be up to 3 times slower than a properly aligned one.

…I formatted both drives using the command “time mke2fs /dev/sdc1” (and sdd1).

/dev/sdc, which was aligned, took 5m 45.716s to format.
/dev/sdd, which was not aligned, took 19m 53.609s to format.

That’s a difference of greater than a factor of three!

The article author conducted several other tests. This is a very good read. Read the full article.

Partition Misalignment Slows Down 4096-Byte Sector Hard Disks by George Notaras is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
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