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Exploring WD's Advanced Format HD Technology
Date: Feb 26, 2010
Author: Joel Hruska
Introduction to Advanced Format
Western Digital recently began to ship a new series of Caviar hard drives that included the company's Advanced Format technology. The new Caviar Green models are nearly identical to their standard brethren, but offer double the cache (64MB instead of 32MB at 1-2TB) and have a different model number. A WD10EARS is an Advanced Format drive; a WD10-EADS is a 'normal' drive. WD isn't marketing Advanced Format much at the moment, but it's important to understand what the technology is and how it works, particularly if you're still running Windows XP.

Understanding Advanced Format

The new data label for Advanced Format drives. Pay attention.

Hard drive sizes are typically given in terms of total storage capacity, where 1 byte = 10 bits. This is sometimes further broken down by the number of platters and the size of each. The first 1TB drives, for example, used five 200GB platters; current-generation 1TB drives use two 500GB platters. These values, however, only refer to the accessible storage capacity, not the total size of the platter itself. This invisible (to the end-user) additional capacity is used to store positional information and for error correction code.

Advanced Format changes a hard drive's sector size from 512 bytes (the standard for the past three decades) to 4K. This allows the ECC data we referred to above to be stored more efficiently. When a 512 byte sector size is used, Sync/DAM and ECC information is stored as follows:

Old and busted...

Each one of those ECC blocks is 40 bits wide; a 4K block of data contains 320 bytes of ECC. Using Advanced Format's new 4096 sector size cuts the amount of ECC and Sync/DAM space significantly. According to WD, it needs just 100 bytes of ECC data per 4096 byte sector under the new scheme, a savings of 220 bytes.

New hotness.

Debunking the Myth of Additional Drive Space
We want to clear up some confusion regarding the near-term benefits of Advanced Format. In Western Digital's whitepaper on the
subject (PDF), the company states that it can "gain approximately 7-11% in disk space" by using Advanced Format. ECC accounts for 5.5 percent of this; the rest is presumably a mix of efficiency gains in other areas. This has been misinterpreted in a number of circles as meaning that an Advanced Format HDD offers more storage capacity than a normal one. It doesn't—or at least, it doesn't yet. A WD10EARS and a WD10EADS have exactly the same unformatted capacity and Windows reports both drives offer 931GB of storage space.

Western Digital isn't lying about the efficiency benefits of a 4K sector drive, but the company can use that space in a number of ways. Smaller platters are one option, larger storage capacity is another, and removing the innermost tracks of the platter is a third. This last contains an extra bonus—because read and write speeds are typically reported as an average, knocking off the slowest tracks would make the hard drive look faster in a benchmark without actually changing performance at all. For now, WD isn't claiming that Advanced Format delivers any particular advantage and AF drives aren't carrying much of a premium, if any.

The Windows XP Problem

Advanced Format drives emulate a 512 byte sector size, to keep backwards compatibility intact, by mapping eight logical 512 byte sectors to a single physical sector. Unfortunately, this creates a problem for Windows XP users. By default, Windows XP creates a primary disk partition at LBA (logical block address) 63, which is one block short of being evenly divisible by eight. As a result of this offset, data is written across both sides of the 4K physical sector boundary. Read speeds and sequential write speeds aren't as badly impacted by the offset, but the impact on small and random writes is murderous.

The good news is, Western Digital has already solved the problem. Those of you who want to use an AF drive in Windows XP can either install a hardware jumper (if you plan to use a single, simple partition) or run a software tool called
WDAlign. Either solution will restore the drive's full write performance, but WDAlign is what you'll need to use if you've created multiple partitions on a single disk. For our test, we compared the performance of a Caviar Black 1TB (32MB cache, 7200 RPM), and an Advanced Format Caviar Green 1TB (64MB cache, 5400RPM) in 32-bit Windows XP. The Caviar Green was tested both properly aligned and unaligned to highlight the impact of not using WDAlign or setting the requisite jumper.

Performance Results, Conclusion

Worldbench 6b2

We focused on three tests out of the Worldbench 6 suite: Adobe Photoshop CS2, Nero 7 Ultra, and Winzip.



Once aligned, the Caviar Green does a reasonable job of hanging with the Caviar Black considering that the latter is a higher-end drive. If left unaligned, the Caviar Green's performance craters; it takes twice as long to run through the Nero 7 Ultra test, is 3x slower in Adobe Photoshop CS2, and takes more than 3.5x as long with the Winzip benchmark. This was not an isolated incident, as you'll see from our File Copy and Sandra benchmarks.


FC-Test is a benchmark that creates and copies files from Point A to B and records the total time. We copied two types of files from the test—MP3's (271 files, 990MB, average file size of 3.65MB) and programs (8504 files, 1380MB, average file size of 162K.) While the MP3 write times take a serious hit due to misalignment, it's the small-file program writes that again kick the legs out from under the Caviar Green. SiSoft Sandra 2010's file system benchmark further confirmed the shape of our analysis, and as expected, random write performance between Aligned Green and Black was almost identical.

Finally, we switched to 64-bit Windows 7 and ran PCMark Vantage on both drives.

Ironically, the performance gap between the Black and the Green is larger here than in almost any of our other tests. The Caviar Black is slightly more expensive (currently listing for $99.99 at NewEgg compared to $84.99 for the WD10EARS. There's also a newer Caviar Black on the market with 64MB of cache and support for SATA 6G. This drive is supposedly faster than our current Caviar Black even when using SATA II, and is retailing for $119.99.

Western Digital has done a good job of providing the necessary tools to ensure that a new Advanced Format drive works under Windows XP; the benchmark results we've shown you are meant to underscore the need to use the utility and/or jumper setting as the company suggests if you plan to use Windows XP. This last scenario seems likely, given that Windows XP is still the most popular OS according to Steam, with 43.81 percent of the market. Since read speeds are much less affected by the misalignment, anyone who buys an Advanced Format drive and plugs it in without reading the instructions could end up bewildered when the drive performs perfectly in some ways and badly in others.

As for Advanced Format, there's not currently much to say. Western Digital believes the technology will prove useful in the future and it's true that after thirty years, the 512 byte sector standard was creaking with age. WD is not the only company planning to implement Advanced Format, but it may be a year or so before we can access the true impact of the new standard. The only thing to be careful of when comparing AF and non-AF drives is average transfer rates. This is not currently an issue, and hopefully it never will be, but a manufacturer that uses AF to avoid using the inner tracks of the drive platters can claim higher average transfer rates without actually increasing performance at all. At $84.99 for 1TB, the WD10EARS is a solid value and we'd recommend picking one up if you want a forward-facing storage solution with solid performance and a low price.

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