Advanced Format “4K Sectors” Explained
Advanced Format “4K Sectors” Explained
There is one least feature included on the Scorpio 750GB we need to take a look at: “Advanced Format” or 4K sector formatting. This feature isn’t exactly new since it was implemented in the Green “EARS” revision but it is an integral part of higher capacity drives. While we will discuss the reasoning behind Western Digital’s (and other hard drive manufacturers) decision to change the default sector size from 512 bytes to 4 Kilobytes (4096 bytes) in the next section, there is a secondary side effect to this feature as well. Basically, using 4K sectors instead of the much older 512 byte sectors involves error correction or “Error Correcting Code” (ECC for short). This feature will also help out “smaller” drives like the Scorpio Black 750GB.
ECC is used overcome the inherent increase in “noise” that is introduced when making platters with higher densities. No matter how precise write and read heads are, the closer the bits are together the higher chances that there will be bleed over from one to another. In a nutshell, the bits are now so close together that when it goes to write in a given bit there is a small chance that the bit next to it will also be negatively impacted. Much like on a CD, ECC is literally additional bits added on to a sector that tells the controller what the data in a given sector should be and how to correct it if there are deviations.
By going to 4K sectors, not only can manufactures use ECC that is more effective (estimated at upwards of 200% more effective) but it also take up less space. The “claim” of taking up less space and yet being more effective may at first seem counter intuitive as it should take up just as much room in 4K sectors as it does in 512 byte sectors and be just as effective.
In the old 512 byte sector layout, each little sector had 40 bytes of ECC clustered at the end which was responsible for that particular sector. On the surface, one would think you would need 320 bytes of ECC for the new larger 4K sector but since the implementation of 512Byte sectors the algorithms behind ECC have become more refined and compact. By going with more advanced algorithms, the new 4K sector layout still requires one cluster of ECC at the end of a sector, but that cluster is now only about 100 bytes in size.
As an added bonus, 4K sectors are not only more compact but also quicker and easier to create and read. Since the hard drive controller only needs to make one ECC per sector but that sector is now 4 times as large, the overall ECC creation is faster. It takes processor cycles to create ECC, so the less time the controller has to work on ECC the more time it has for doing OTHER things. Western Digital estimates there will be a 7 to 11 percent real world increase in ECC read / write performance with a huge 50% increase in burst ECC speed.
Years ago when storage size was actually at a premium the less “waste” you had between files, the more room you could use. This additional wasted space was called “slack space” and was essentially useless as it couldn’t be used. Moving to 4K sectors obviously means more slack space, but with monster-capacity drives it no longer matters since physical storage space has been gradually reduced in overall cost.
Sadly, not everything is wine and roses with 4K sectors and the additional wasted space is not the biggest down side of them. The biggest downside is the potential performance impact of 4K sectors when used in conjunction with older operating systems.
As any SSD user will tell you, XP does NOT use a “proper” offset when it formats a drive since it uses a less than optimal 63bit offset. This was perfectly fine in the past but on any storage device that uses 4K sectors, this offset will cause issues since a single 4K write will use two sectors instead of one.
Western Digital has had some time to work out multiple solutions to this issue; one of which is through the use of a simple jumper pin. By inserting an included jumper, the hard drive will do a logical offset correction. The upside to this is XP will specify an improper offset of 63 and the drive will automatically set about writing correct offsets. The downside is once you set the jumper you MUST use it unless you want to reformat your drive. In addition this method is only used for 3.5” hard drives since the jumper pins on 2.5” drives like the Scorpio Black are for Spread Spectrum Clocking (“SSC” via jumper pins 1 & 2) and Reduced Power Spin-up (“RDS” via jumper pins 3 & 4).
Since the jumper pin method is not available for some drives, the only options are software based solutions offered by Western Digital.
Basically, they offer two partition managers (one from Acronis and one from Paragon) which will check the offset of a drive and either fix it (without being data destructive) or keep things as they are if no problems are detected. It is fast, easy and extremely easy to use.
Luckily, this issue was fixed since Vista SP1 so only XP users need worry.
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