Western Digital introduces 'Advanced Format'
Subject: Storage | December 11, 2009 - 10:04 AM | Allyn Malventano
I was recently briefed by the fine staff over at Western Digital about their new 'Advanced Format' partitioning scheme. This is a new format method they will be incorporating into their various drive lines. Advanced Format represents a new way for their drives to handle data internally. Instead of each individual sector having its own Sync/header and ECC, the new format will move to larger physical sectors, in this case 4k. This results in an overall net gain in storage efficiency, so much so that Western Digital was able to save on wasted space even after shifting to a larger ECC block size. Larger ECC is a good thing, as Error Correcting Code is used to detect and correct bit errors that occur within each physical sector. The new ECC block size should translate to a 50% improvement in error correction ability. Here is a look at the new format as compared with current tech:
Bear in mind this takes place at a very low level and therefore can not be applied to any current drives (i.e. via firmware). While Advanced Format yields roughly 10% net gain in usable space, Western Digital will be sticking to the round number capacities existing in all current lines. I would have loved for them to use this as an opportunity to move from terabytes to tebibytes, finally bringing hard drives capacities in-line with other computer related capacities, but I'll just have to keep dreaming on that one.
There are a few things to consider with this move. Since the sectors are still logically 512 bytes each, a 2TB drive will still have the same number of sectors as before (just shy of 2^32). Advanced Format will therefore not do anything to correct the difficulties Windows XP and older legacy operating systems have addressing drives larger than 2TB.
Another slightly more important catch is that a modification to a single sector requires the entire 4k block to be read, modified, and then written back to the disk. Seasoned RAID and SSD users are used to this sort of thing, as RAID stripe and SSD block erase sizes are typically multiples of 4k or higher. Increased use of RAID was what led Microsoft to change the default partition start from sector 63 to sector 2048. This change started with Vista and is included in Win 7. Those still running XP with a default partition will see a performance hit with these new drives, as each 4k cluster modified will not be properly aligned to the 4k blocks of the Advanced Format drive. Because 63 is not evenly divisible by 8, each 8-sector cluster written will result in 2 4k blocks modified on the newer drive. Here is a visual of what takes place during a single cluster write with an incorrectly aligned partition:
Note how the writing of a single cluster 'spills over' into two physical clusters of the Advanced Format drive. The same type of thing happens with an incorrectly aligned RAID or SSD as well.
WD have provided two options for those under Windows XP:
- Use the 'WD Align Utility' (provided here), to re-align pre-existing partitions.
- Install a jumper between pins 7-8 on the drive prior to use.
The utility was co-developed by WD and Paragon. It is able to align attached external drives as well as the OS drive itself and is available in both 32 and 64 bit versions. Installing a jumper between pins 7-8 on the drive does nothing more than direct the drives firmware to offset the LBA by one (i.e. sector 63 becomes 64 as far as the drive-side of the data is concerned). This would cause a default XP partition to perform as if it was aligned properly. You can't shift this jumper after data is present on the drive as it would cause the Partition Table / Master Boot Record to be offset by one sector as well and therefore cause it to be unrecognizable by the OS. Amplifying instructions will be present on the new drives, including a brief explanation of jumper use:
An example of the new label verbiage.
WD will be rolling out the new 'EARS' variant of the Caviar Green line over the next few weeks, and will eventually incorporate the technology into many of their other product lines. The full white paper on the subject is available here.