Solid state of the nation

10th May 2007 | 23:00

Solid state of the nation

NAND flash technology has come of age

There's nothing that Seagate, Hitachi or Western Digital can do about it.

Those giants of the spinning disk world must be quaking in their boots. The flash storage revolution is coming and it could well wipe that last bastion of ancient mechanical technology from the face of the PC world.

Opto-mechanical drives have always been an aberrant part in the PC. Despite the perfection of their mirrored spinning platters, the hard drive - even the latest 750GB capacity gorgons - is a real performance bottleneck, not to mention a serious power drain when it comes to mobile systems.

A replacement for hard drives has been expected. In the past we have looked at two of the early solid state drives and found them lacking, though at the time we said the promise of performance was there. Today, with Intel and Samsung getting into the act with hybrid drive technologies and entire replacement drives; the solid state drive is here.

Flash bang

We're all familiar with NAND flash technology. USB thumb drives, memory cards and music players like the iPod Nano all use NAND-based flash memory. It's a cheap, solid state memory technology that's suited to a storage role, as it's accessed in a sequential manner with data stored in blocks of pages.

It has higher access speed than other solid state technologies - such as NOR - and a longer lifespan of at least a million rewrites, if not three million plus. As with spinning disks, NAND-based drives can suffer bad blocks.

Error correcting and bad block mapping can be performed on the fly; when a bad block is detected it'll be marked and won't be used again, and data will be moved to a free area. Flash chips are grouped together to build up capacity.

Currently Samsung is producing individual 8GB chips, and these can be used together to produce drives of higher capacity. It seems four is optimal, with Samsung opting for a 32GB IDE flash drive, while has a 128GB drive that utilises a SATA interface in a 2.5-inch drive package.

Using Moore's law as a guide 2,568GB and 512GB flash drives should be common by 2010,and be large enough for a system boot drive. Fast access times are a feature, even early devices showed access times in the points-of-milliseconds level, compared to traditional drives that peak at ten milliseconds.

Spinning discs can only read what's currently under the single read head array. If it misses the data, the platter makes another revolution, that's on top of the time taken to get the head into position initially. There are a few very common situations that cause spinning drives real trouble because of this behaviour. The first is when it's trying to load lots of small files dotted all over the drive.

The second is trying to deal with a badly fragmented drive. The third is when multiple tasks are trying to access data from all over the drive. All of these result in drive thrashing. If this is happening, a drive with a sequential speed of 100MB/s plus is pointless. Flash memory with a random access speed a hundred times faster than a traditional drive, can cut through these tasks easily.

Robson lives

With the capacity now making a difference to drive speed, the question is how to implement it, as the unit price is still high. This has resulted in a hybrid solution that's available now in different guises. We'll be hearing a lot about Turbo Memory - previously known as 'Robson' - part of the new Centrino Duo and Pro architecture that we've already reviewed .

The idea behind it is the same as the ReadyBoost technology in Vista and the Samsung 160GB hybrid drive, you take a reasonable-sized lump of flash memory and use it to cache often accessed files.

Demos from Intel show it can increase real world application performance by 100 per cent. As the Turbo Memory allows the hard drive to be spun down more often, it'll improve battery life and drive reliability, as allowing drives to power down reduces the risk of head crashes while moving the laptop in use.

Intel doesn't state Turbo Memory works faster than ReadyBoost. It does stress that for mobile platforms ReadyBoost can't offer any power savings or indeed be used to cache any permanent files - such as the swap file - as Windows will see the USB key as a removable device, while Turbo Memory is permanent.

The solution's success depends on the quality of the caching algorithms, but such things tend to be very well known. The other is the size of the cache used. The Samsung hybrid is 128MB and 256MB, Turbo Memory is offered in either 512MB or 1GB while ReadyBoost tops off at 4GB.

Intel couldn't answer why larger Turbo Memory modules aren't offered, as 2G or 4GB could be supported, it may be being held back for the future; perhaps the increase speed doesn't justify the cost; or maybe Intel's fear that by the time the costs have dropped, full-sized flash drives will make it irrelevant.

Final solution

The final solution will be full solid-state drives or SSDs. Samsung has the 32GB Flash SSD. Using four 8GB flash memory chips, it's packed as a standard 2.5-inch 40-pin PATA hard drive supporting UDMA66. It's an odd mix (why no SATA?) and not destined for mainstream systems at the moment, this won't last long: Samsung's figures show it expects to shift around 1.7 million SSDs in 2007, increasing to 90 million in 2010.

A driving factor is SSDs are near impervious to vibration, shock and high temperatures, and the lower power consumption. Tests showed total laptop power consumption dropped from 26W to 22W - under heavy drive use - by switching a 7,200rpm drive to the SSD.

While the advantages of solid state drives are clear, we're currently in a transitional period. Hybrid drives, Turbo Memory and ReadyBoost all promote this emerging technology. Even when large enough SSDs are used as primary boot devices, it seems better to retain a larger capacity optomechanical drive as storage. So while their role may be relegated to storage and back-up, our spinning friends will still be around for some time. Words: Neil Mohr


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