Exploring WD's Advanced Format HD Technology - HotHardware

Exploring WD's Advanced Format HD Technology

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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.

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Do you guys think that WD will enable this technology for the Black drives at any time?

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Anytime?  Definitely. My guess is that WD went ahead and did the Caviar Green drives first because it was a change that could be easily slipstreamed into the 64MB cache versions of the disk. 

The Black series just got a refresh; the new 64MB cache drives are a fair bit faster than the old 32MB and they offer SATA 6G. I'm betting we'll see Black AF drives the next time WD refreshes the product series.

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It'd be interesting to see how a SATA 6G Caviar Black drive with this new feature and the 64 MB cache fared against a SATA 3G SSD. If the results were close, it could mean new life for mechanical HDs (though I'm sure a 6G SSD would beat the tar out of them).

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At least from early benchmarks I've seen and based on current hard drive technology, I don't think this improvement will be anything too far (in performance) from what we see today in traditional platter drives. Aren't the Caviar Black drives not even reaching anywhere close to the 3 GB/s that the "older" SATA offers? I don't think there will be much difference from a 3 GB/s to a 6 GB/s platter drive. Maybe, though I still don't think so, there might be some difference when in RAID.

I think any real improvement in the platter drive would be to make a huge cache (in GB), which is basically like that hybrid design that Silverstone came up with. Other than that, I think SSDs are the way to go in terms of pure performance.

From my understanding, I think the main reason for this Advance Format is to make it easier to produce higher capacity hard drives. Correct me if I'm wrong.

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Clem,

I think you're confused on a few points here--let me see if I can help.

Performance: Neither SSDs nor HDDs can keep 6Gbps of bandwidth fully saturated right now. The difference is that mechanical hard drives will likely never be able to pull this off. The gap between SSD and HDD performance is variable depending on what sorts of benchmarks one runs (and SSDs don't always have a huge advantage), HDD's leverage their tremendously lower cost-per-GB vs. SSDs, not raw performance.

#2. SSDs generally are the way to go for pure performance, but unless you've got a hugely fat wallet, price inevitably comes into play. This is where things currently get sticky--there are a variety of drives and controllers on the market with a huge variety of performance. If you can afford to spring for an enterprise-class, $800 SSD (or two in RAID), yes, it'll blow an equivalent $1600 HDD performance setup out of the water and it'll draw a lot less power. If, on the other hand, you're trying to balance price and storage and don't want to spend more than $150, a new Caviar Black [insert manufacturer of your choice here] will be the better option.

There is a definite diminishing marginal return that makes "building a huge cache" a bad idea past a certain point. Remember, the entire point of a cache is to provide the system with a low-latency/high-bandwidth storage area in which only highly relevant data is stored.

The more cache in a system, the longer it takes to search it and the more unwieldy it can be to maintain. The more time the drive has to spend keeping the cache updated and filled, the greater the chance that the end-user will actually notice performance degradation.

Finally: There is no one "main point" to AF. It does or enables a series of options; the larger disk drives is just the simplest to understand.

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I don't think Clem is confused, his posts are generally on different things than what you are talking about in some points. Also the cache depends largely on how it is handled. Yes SSD's are the way to go for pure performance to a point. However; a system that is focused on performance alone, will also to some points not be the best, because everything is focused on performance alone, and therefore usability is sacrificed. I personally am currently running 2 WB black 32Mb cache drives. However right now I don't have them in a RAID configuration because to the greatest point it is not really necessary.

I am currently thinking about grabbing a SSD for one thing and one thing only which would be main app's, the largest would of course be the OS, and a dual system image backup to the SSD, and to the converted RAID0 with 2 WD Caviar Black 750GB drives. Of course I have not implemented it yet I think this would be the best combination. I would have speed from the SSD platform; I would have space from the RAID configuration, and would also have performance with it being Raid 0.

As for your comments on a HDD catching up to and SSD you are 100% correct that will never happen. Also on top of this SSD's are new devices, and will therefore be upgraded for quite some time, this is very valid in this discussion because we are basically talking about the first large storage format HDD in a commercial market Vs. a brand new one, and the old one is as in this article still being upgraded.

On the more cache thin and the implementation thereof someone mentioned one thing in this conversation which I think is very valid. The combination of an SSD for speed and cache duties and a modified HDD into a singular device seems very promising. This would and could be very nice on all ends, but I think the controlling scheme as well as software firmware etc needs a good bit of work to find the most efficient, and speedy implementation scheme. This in many ways is much like I am saying I may do on my PC, with the RAID 0/SSD setup where the most active programs and software will be on the SSD for performance, the rest on the HDD for its capacity and relative speed in a RAID 0 2 x  750Gb 7200 drive scheme.

 


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Ah, thanks, Joel. Wasn't what I was asking, but thanks for the reply.

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Bout time, now if they can just give us adjustable speed up to 10-12K! Without killing us for the comparable size.

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Joel, do you know if WD have put something in their WDAlign tool that prevents it from being run on non-WD drives?  If not, then this tool could be a godsend for people with mis-aligned SSDs.  Aligning an SSD for XP use can sometimes be quite awkward, so if this could do the trick I'd be delirious.

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"A WD10EARS and a WD10EADS have exactly the same unformatted capacity and Windows reports both drives offer 931GB of storage space."

 

That does not debunk the myth as I understood it. I have read that the "usable space" is affected. Meaning that if both drives are filled with files. The WD10EARS will be able to hold more files/more data. That is because it is more efficient at storing information. Am I correct?

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