Advanced Format

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Revision as of 21:54, 17 July 2010 by Graysky (Talk | contribs) (Current HDD Models that Employ a 4k Sectors)

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The 'advanced format' feature reduces overhead by using 4 kilobyte sectors instead of the traditional 512 byte sectors. The old format gave a format efficiency of 87%. Advanced Format results in a format efficiency of 96% which increases space by up to 11%. The 4k sector is slated to become the next standard for HDDs by 2014.

More Detailed Explanation

512-byte sector size standard is here for over 30 years and therefore lots of the code written for a Linux OS has 512 number hard coded in its source. The main idea in regards to the 4096 B size sectors is to increase the bit density on each track by reducing the number of gaps which hold Sync/DAM and ECC ( Error Correction Code ) information between each data sectors. Therefore, for 8 x 512 B sectors the track also holds 8 sector gaps.

By having one single sector of size 4096 B (8 x 512 B) the track holds only 1 sector gap for each data sector thus reducing an overhead for a need to support multiple Sync/DAM and ECC blocks and at the same time increasing bit density.

Linux partitioning tools by default start each partition on sector 63 which leads to a bad performance in HDDs that use this 4k sector size due to misalignment to 4K sector from the beginning of the track.

External Links

Current HDD Models that Employ a 4k Sectors

As of July/2010, there are a limited number of HDDs that support "Advanced Format" or 4k sectors as shown below:

Manufacturer Model Capacity
Western Digital WD10EARS 1.0 TB
Western Digital WD15EARS 1.5 TB
Western Digital WD20EARS 2.0 TB
Note: Readers are encouraged to add to this table.

Aligning Partitions

One can employ fdisk to align partitions to sector 2048 which will ensure that the partitions are aligned to the 4k sector. Interestingly, in sector mode, the default starting point is not 63 or 64 but 2048 in the current version of fdisk (2.17.2) so it's automatically taking care of the 4k sector size!

# fdisk -c -u /dev/sda

Special Consideration for WD Green HDDs

FYI - this section has nothing to do with Advanced Format technology, but this is an appropriate location to share it with users. The WD20EARS (and other sizes include 1.0 and 1.5 TB driver in the series) will attempt to part the read heads once every 8 seconds FOR THE LIFE OF THE HDD which is just horrible! Use hdparm in Template:Filename to disable this 'feature' and likely add life to your hdd:

# echo "hdparm -S 242 /dev/sdX" > /etc/rc.local

Alternatively, the following bash script can accomplish this automatically:

for DISK in `fdisk -l |grep 2000.4 | cut -c13-13`
do echo hdparm -S 242 /dev/sd$DISK
#note you need to substitute 1000.2 in for 2000.4 if you have a 1 gig version