4K Advanced Format Hard Disks

The Facts: 4K Advanced Format Hard Disks



We're sure you've heard the hubbub about the upcoming 4K Advanced Format for hard disks, especially as it's likely every new high capacity hard disk product shipping by the end of this year will feature this new sector size. Western Digital saw our news piece and the many comments you, our readers, and got in touch to clarify what the new standard actually entails.

A lot of hot air has been ejected recently about 4K AF's incompatibility, or that 4K AF disks will slow down beyond a usable state in Windows XP systems, one person even moaned that, 'Western Digital said I'd get 7-11 per cent more space, but I don't get anything!' A lot of these frustrations are just simple misunderstandings or bogus statements.

WD wanted to explain that the hard disk industry is not necessarily releasing 4K Advanced Format drives for consumers (hence the subtle product launches, rather than fanfares and huge marketing campaigns). The 4K Advanced Format move is actually a fundamental upgrade needed to ensure future capacity increases - and by extension future performance gains - are capable, rather than a move to deliver any tangible benefit now.

While we're relating to Western Digital a lot in this article, it's worth remembering that the whole hard disk industry will be changing this year. Western Digital is not alone in launching new 4K Advanced Format products; other hard disk companies will follow suit this year, although WD was the first with its 'EARS' Green drives last December in the UK market.

What exactly is a sector size?



Since the floppy drive, disks have been split into sectors, each allocated in 512 byte blocks, with an associated error correction control (ECC) portion adjacent to each sector. This has worked fine for the last 25 or so years, and increments in hard disk data density have been achieved with various inventive methods. It's incredible to think that we've gone from 1MB disks to having 500GB on a single 3.5in platter using the same basic division of storage. However, the hard disk industry has now reached a point where it's no longer economically viable to keep such tiny sectors on such immensely dense hard disk platters.

4KB data sectors have a few advantages: the combination of eight 512 byte blocks with ECC takes up more space than a single 4KB block with a single, if larger, ECC area. This means moving to a disk platter comprised of 4KB data sectors allows more data to be stored in the same physical space (as there’s less room wasted on ECC portions). A larger ECC area also allows for the use of longer code words, which are more efficient.

Thirdly, ECC itself has been refined over the last 25 years, and the algorithms can now cope with larger ECC sectors. Finally, there is an element of backwards compatibility, as the 4KB sector size is used in modern File Allocation systems such as NTFS (first used by Windows NT 4.0 in 1996, and still used by Windows 7 today), and is divisible by other modern file structure formats such as FAT32 (the common standard of Windows XP, even though it supports NTFS).

Do I get more space for free?



Western Digital stated that, depending on the product, moving from 512B to 4KB layout gives drive manufacturers about 7-11 per cent more physical space on the platter to work with. Note that that's physical space - as a customer, we won't see free extra storage space from your drive. Furthermore, you cannot convert your current drive into a 4K Advanced Format drive, as this requires an updated disk controller with slightly different hardware and corresponding firmware. Whether it’s a 4K Advanced Format disk or not, if you buy a 2TB drive you still get two trillion bytes and lose the same amount as usual when formatting to NTFS.

If the 4k AF gives hard disk manufacturers more space, where does that go? The answer is future proofing. Hard disk companies are currently expanding the 4KB sectors to match the size of eight 512 byte sectors to give these sectors some ‘breathing room'. This means that the data density of current-generation drives remains the same as for non-4K Advanced Format disk, and performance is unaffected too. However, for future generations of 4K Advanced Format disks, platter capacity can again increase without the need for hard disk manufacturers to implement costly new techniques.

The good news is that as platter capacity rises, you get faster data access times and improved performance. And this comes with the added benefit of no significant price increase and a real possibility of a fall in price per GB.

Are 4K Advanced Format drives any faster?

To put it bluntly: no, not right now. If we take the Western Digital Caviar Green (EARS) disk, the platter density and spindle speed is the same as that of other Green hard disks, so the read/write head still covers the same amount of data in a single rotation. Western Digital claims about 1-2 per cent performance increase over previous 2TB Green hard disks (confusingly, there are three models on sale at the moment), but that can also be attributed to the increased cache size of this disk from 32MB to 64MB, not its use of 4K AF.

The extra cache is predominantly required for multiple storage-process streams, but also helps because of the fact the 4K Advanced Format introduces a Read-Modify-Write scenario in 512B OSes. For example, if the OS issues a write to a 512B sector within a larger 4KB block, the drive has to first read the whole 4KB block into cache, modify the data within the cache and then re-write the whole block. Unlike an SSD however, because a hard disk can only access a single area on the platter at any one time (versus multiple cells of NAND flash memory), this takes two disk revolutions. However, Western Digital claims that this process doesn't impact performance, and that it’s invisible to the OS.

Western Digital also explained that cache sizes on a hard drive will always remain relatively small versus SSD capacities because on sudden power loss the drive needs enough time to dump the cache to the disk’s platter before it starts to slow down and lose synchronisation. The synchronisation Western Digital is talking about here is the link between where the read/write head thinks it is in relation to data sectors on the disk and where it actually is. If the platter starts to spin at an unknown speed (say, slightly slower than normal, because the drive has lost power) the read/write head will think that it’s somewhere that it’s not and could not only overwrite important data, but won’t know where to look for the dumped data when power is restored.

Will it break Windows XP compatibility?

Test Setup: Windows 7 and Windows XP4
ATTO Disk Benchmark5 -
IOMeter Benchmark6 -
AS SSD and 4k Performance

Windows XP and other older OSes work by accessing specific disk sectors, not by using 'atomic writes' that work on byte-level data placements that we see in Windows Vista, 7, Server 2008, MacOS 10.4, 10.5 and 10.6 (Tiger, Leopard and Snow Leopard) and recent Linux kernels from 2.6.31 onwards.

Windows XP (and Windows 2000 and Server 2003) use a method of accessing the hard disk that starts at sector 63. Because 4KB sectors match eight 512B sectors, sector 63 is unfortunately is one sector shy of being directly compatible, so using a 4KB data sector with these OSes causes mis-aligned writes.

The Western Digital EARS disk has the option (via a jumper on the back of the drive) to implement a hardware-level '+1' on every OS sector request. This means that if the OS requests Sector 63, the drive actually chooses Sector 64, and sector 1,090,203 from the OS becomes Sector 1,090,204 on the drive. This jumper-based workaround might not be the same for every 4K Advanced Format disk from every manufacturer, so check the manual and manufacturer’s website before you buy if you're using an older OS.



For those who want multiple partitions, for example those who dual-boot, things get a little more complicated as the old OSes do more convoluted things that the Western Digital drive’s firmware can't easily compensate for. When using partitions with a 4K Advanced Format disk on an OS that might have issues with it, WD has created an application to run in the background that will avoid the slow-downs that people have been reporting.

Are there any other limitations?

Certain types of hard disk software needs to support the 4K Advanced Format - this includes cloning software and low-level formatting software. If you want to image your installation to a new disk, or completely wipe a 4K Advanced Format drive, then you need to check compatibility before use.

RAID controllers are generally unaffected because they simply see stripe sizes and the disks as a whole – it’s the OS that directs where it thinks the reads and writes should be taken from. However, multiple partitions within RAID arrays might suffer the same consequences as above on sector-driven OSes, so again the background software might have to be used. Western Digital said that it cannot possibly test every setup for niche arrangements on older OSes, hence the ‘mights’ and ‘maybes.’

We asked about JBOD setups, and Western Digital claimed these only require the jumper workaround, as the whole drive is used as a single partition. That's good to know for the many people looking to upgrade Windows Home Servers (based on Windows Server 2003) with increasingly larger drives in the future.

What does the 4K Advanced Format do for me then?

Right now, not much. It's not a marketable feature that drive manufacturers are pushing and branding because there's currently little tangible benefit to the consumer. It simply eases the pressure on the fundamental data storage technique for hard disk manufacturers that will allow future platter capacity increases, which will then bring us benefits.

However, we would like to see clearer labelling on 4K Advanced Format disks, as this could influence whether you buy the disk or not (perhaps you are still Windows XP, or plan to put the disk in a Windows Home Server). It’ll also help you to know to check that any storage software you plan to buy (cloning or deep-level formatting) is compatible with your new disk.

Windows 7 Testing Setup

* Intel Core i7 920 (operating at 2.83GHz – 21x135MHz) - TurboBoost and power saving states disabled.
* Gigabyte X58A-UD7 motherboard (Intel X58 with ICH10R southbridge, USB 3.0 and Marvell SATA 6Gbps)
* 3x 2GB Corsair XMS PC-1333 memory
* Nvidia GeForce GT 240 512MB
* PC Power & Cooling Silencer 750W PSU
* Windows 7 Home Premium x86-64
* Nvidia Forceware 196.21 WHQL
* Stock Windows AHCI driver (msahci.sys)

This is our standard Windows 7 test system that we use to test all hard disks and SSDs.

Windows XP Test Setup

* Intel Core i5 750 (operating at 2.66GHz – 20x133MHz) - TurboBoost and power saving states disabled.
* Biostar TH55XE motherboard (Intel H55 PCH)
* 2x 2GB Kingston 1,600MHz DDR3 memory
* ATI Radeon HD 4530 512MB graphics card
* PC Power & Cooling Silencer 750W PSU
* Windows XP Home 32-bit
* ATI Radeon Catalyst 10.3 WHQL

The Facts: 4K Advanced Format Hard Disks Test Setup: Windows 7 and Windows XP

We have compared whether using the '+1' 7/8 jumper makes a noticeable difference or not, and we have tested the effects of multiple partitions - testing each partition after the WD Align software had run. We also compared all this to a standard 512B sector size EADS disk with a single partition.

Performance Analysis

Performance in Windows 7, where the drives are natively accessed in 4KB sectors, saw a doubling in performance in 4KB read and write over the older 512B drive. In fact, the new EARS disk was almost universally faster than the old, non-4K Advanced Format disk in every ATTO test when using Windows 7. Only in the 1,024KB sequential write test was the new disk slower.

In Windows XP the situation was pretty much the same, although the EARS disk was faster under Windows XP once we’d applied one of the workarounds to the disk. The 4KB sequential read speed rose from 59.8MB/sec to 62MB/sec and the 64KB sequential reads from 96MB/sec to 112MB/sec, to cite two examples. Note that when we used the drive with no workaround applied (Profile 1), the EARS disk was much slower in every test than when we applied some kind of workaround. We saw no significant drop from using multiple partitions on the EARS disk under Windows XP either.

In Iometer, we saw identical random write speeds and latencies from the two disks when using Windows 7. However, the new EARS disk was much slower than the old EADS disk when it came to random write speeds, with a poxy 0.12MB/sec rather than 1.12MB/sec, and it showed much higher random write latencies of 98ms rather than 11ms. This could be due to the read-modify-write nature of the new disk, as Iometer is designed to work with XP and so loads drives with random 512B chunks

In Windows XP, the situation doesn't change, and the more recent EARS drive still suffered in write latency and performance. We saw quicker average random read latency when using multiple partitions on the new EARS disk, but the difference is of a few milliseconds and so academic rather than noticeable. We saw no significant change in any other test scenario.

One thing that hit us while testing was how slow the new EARS disk was after installing Windows XP before running the WD Align utility. The installation took notably longer than usual, and the disk ground to a complete halt when tried to install the chipset drivers upon the completion of the OS install. Rebooting and running the WD Align straightaway cured the issue, and we didn't need the software at all after that. Every time a new partition was created, the WD Align utility had to be run, but at least it only had to be run the once, and not continually as a background service.

Conclusion

The performance loss in Windows XP was negligible in every scenario, which is great news for those still clinging onto it. There’s even evidence to show that the new disk will be faster under XP than Windows 7. Naturally, in 4KB reads and writes there’s a huge performance advantage for the newer 4K Advanced Format disk, but at the same time the write latency has taken a hit. In our tests, we found the jumper workaround for Windows XP to work perfectly fine, and we didn’t have many issues with setting up partitions on the disk either.

Disks based on 4K Advanced Format are a natural evolution to the old 512B models, so to some extent, 'should I get a 4K AF disk' is a moot point - it's what the industry is moving to in order to give us more density per platter and cheaper (or at least no more expensive). As higher capacity and increased areal density often results in better performance, there's a speed benefit too.

The caveat is that you won’t see those benefits just yet – the standard is being introduced this year so that it can enable disks of the future to deliver these advantages. We'll have to wait to see whether the 4K Advanced Format change will make a tangible difference.

Author: Richard Swinburne
Published: 1st April 2010
http://www.bit-tech.net

I really got to upgrade my hard disc. This thing makes me drool over my keyboard. I had to delete gigabytes of oblivion mods to free space from 15% free space to 26% free. I only have a 80 gig hard disc lol

Hehe i know how you feel!
I have a 40gig hdd which is split into two, one partition for windows for gaming, and the 2nd is for Ubuntu for surfing the net. I went and bought a 500gig external hdd to solve the problem but really need to get another internal drive one day.

Me too, I've been living off an 120 GB for years now. A big fat 1TB internal drive would be really nice for downloading.

I've got a 500GB SATA 2 drive and its been working nicely. Another one would be nice of course.

I'm not sure about Solid State Drives. I think Project Honey Pot spent loads of transferring their site to them and a few months later they broke down.