The Barracuda Green 2 TB is Seagate’s first hard drive to use 4 KB sectors instead of 512-byte sectors. The new standard, also known as “Advanced Format” or simply “AF,” will be used by all hard drive manufacturers in the future. Let’s see what are this new format and the performance of the Barracuda Green 2 TB drive.

The hard disk drive magnetic platters are divided into sectors. Each sector has an area before (addressing information) and after (error correction code, a.k.a. ECC) the data area to store control information. These areas occupy space on the platter, but this space is not available to the user. By expanding the size of the physical sectors on the hard drive platter, fewer areas for control purposes are necessary, leaving more area available to the user.

In the new Advanced Format, sectors can store 4 KB of user information, so one 4 KB sector stores as much as eight 512-byte sectors. This means that instead of having eight pairs of control areas, the new 4 KB sector has only one pair. The seven pairs of control areas that were freed by each 4 KB sector can now be used to create more sectors on the disk. See Figure 1 to understand. Therefore, a platter using 4 KB sectors can have more sectors than if the same platter were using 512-byte sectors. In summary, the Advanced Format allows the same platter to hold more user data, i.e., have greater capacity.

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Figure 1: The difference between using 512-byte and 4 KB sectors

Ideally, the hard drive must have a translation mechanism to improve performance when the hard drive receives write commands based on standard 512-byte sectors from the computer. If not, the drive will have to read the entire 4 KB sector, update the 512-byte portion that was sent by the computer, and then write the entire 4 KB sector back on the drive. This situation, called “read-modify-write,” degrades performance a lot; according to Seagate, this performance drop can be as high as 40%. In the Barracuda Green 2 TB, Seagate added a translation mechanism called “SmartAlign technology” to address this issue.

More information on the new Advanced Format can be found here.