Next-gen storage that makes SSD look slow

28th Jan 2010 | 12:21

Next-gen storage that makes SSD look slow

Speedy alternatives to the humble hard drive

Your hard drive is the bottleneck

A quick look through the bus speeds and data rates available in a PC system soon tells you where there is a bottleneck: it's your hard drive. All over the board data is being shifted in gigabytes per second, but the hard drive is still doing it in megabytes.

Theoretical speeds aside, what you're probably getting is 50 to 70MB/s, tops, and you'll have to wait while it finds the data in the first place.

Hard drives have been a fundamental part of the PC for yonks. The interface has changed and capacities and speeds have marched ever onwards, but essentially its pretty much the same device that graced IBM's new-fangled computer things in 1956.

Every time it appeared as if the edge of the technology had been reached, some development or other comes along to push it further. Giant magnetoresistance heads, often cited as the first practical application of nanotechnology, came along in 2000 (and won its inventors the Nobel Prize).

HDD

In 2005, we got perpendicular recording (the magnetic regions are arranged vertically rather than end to end). All this engineering effort meant for years now data densities on the platter where growing by 100 per cent a year, without prices doing the same. Now a typical drive of 500GB or 1TB costs about £50, give or take.

All well and good but capacity ain't everything and, fast as they are, the traditional hard disk drive has a basic design, which simply cannot be made to run at the sorts of speeds the rest of your system can cope with. If sheer capacity is paramount then ye olde hard drive reigns supreme. For oomph it is time to move on.

So Solid State

Enter the cocky solid state drive to step all over the old guard, sporting no moving parts and access times a spinning disc could only dream of.

From its origins in server and racks, through USB keys, we now have solid state drives that plug straight into SATA, so you can simply plug them in and off you trot. Instead of all that moving about gubbins you've a mass of non-volatile NAND flash memory. Great stuff, problem solved.

SSDs are excellent at random reads, there's no disc head to position, it'll run a hundred times faster than its mechanical cousin with random access times of about a tenth of a millisecond versus up to 10 milli-seconds. Sequential reads run at 150 to 200MB/s, double or more that of a typical HHD. Sequential write isn't quite as impressive (more like half that of early drives but getting better now), it takes a 10,000rpm HDD drive to put up any competition here.

SSD

Rather surprisingly though, it transpires that solid state drives wear out. The floating-gate transistors can only stand so many read-write cycles: 100,000 is typically quoted. Sounds like a lot but that's not quite as much as you might think, given the number of writes made during a few hours browsing.

Don't be too scared of the limited life though, drives sold with a guaranteed 100,000 cycle life means that nearly all the little fellows will last considerably longer. Clever jiggery-pokery with the controller helps spread and minimise the load and patch over any errors too.

True, it won't last forever, but this is PC technology we are talking about. Capacities fall a long way short of HDD and prices per GB remain daunting: Around £100 currently secures 64GB - sufficient for a Windows installation, an application or two and some data to play about with, but that's it. You can always use a big fat hard drive as an adjunct if you insist on going mad and having loads of films, music and games on your PC (you crazy fool).

However this means two drives where we really want one. Even with larger capacities and lower prices, SSD still doesn't write fast enough and however clever you are controlling it, the NAND memory currently has a limited life.

Using RAM drives for ultimate performance

Main memory speed is what we are really after, so why not use a drive composed of full-fat RAM in the first place? The idea dates back to the late 1970s, when discs were floppy, made grinding noises and were achingly slow.

These days you can get drives that plug straight into your SATA controller and are fitted with DRAM modules and a battery. You'll need the battery because otherwise everything evaporates when you switch off; a fundamental problem.

These things are fast, though - fast enough to virtually swamp your SATA interface, murdering all the competition; they can shift gigabytes per second and random access time is in the 0.0-something range. So, its quick.

RAM

The first snag is felt in the wallet. RAM is expensive and you'll want a ton of it. Even the biggest modules are small in the world of storage. Fill eight slots with 2GB modules and that's a painful £200 minimum, before you've bought your RAM drive (£200 and up). After all that you've still only got a 16GB drive, barely enough for Windows and a couple of friends; hardly an HDD replacement so once again we are running two drives.

Another major snagette is that to keep the data you need constant power, either an external supply, a small battery pack or some other storage to back it up (some flash RAM works well).

RAM takes a fair amount of power to keep fresh, a battery of twice the oomph of a mobile phone gives about 16 hours. If you've installed Windows then an external power pack is best. The data risk loss is unacceptable for a single drive system and limits RAM drives to the specialist role. Still, speed is alluring isn't it?

A RAM drive is currently the canine orbs of performance, hundreds of times faster than the best mechanical devices. Whack Windows on it and or use it as a scratch disc for Photoshop or other such drive intensive jobs and you get a nice bang for your (not inconsiderable) buck.

A RAM drive is a better bet than shelling out an extra couple of hundred to get the next best processor up the ladder and well worth considering if a fast PC is your bag (if it isn't you might be reading the wrong mag).

Ideal world

The latest fastest spinning HDDs remain attractive, they may get hot, consume lots of power, make a fair bit of noise, but they can shift really big blocks of data effectively and a terabyte is a terabyte after all.

Running an SSD, instead, is great for machines that aren't expected to store a ton of data, (fiddly little notebooks), and they make an excellent partner for a fat HDD in desktop. If you feel adventurous and slightly rich then adding a DDR RAM drive gives you the ultimate in performance.

We want the capacities and prices of traditional hard drives, the non-volatile nature of SSD and the pure speed of main memory RAM. Well, you can't have that, yet. But there are plenty of people toiling away to bring it to you.

There are a good dozen new memory technologies in the wings - MRAM, CBRAM, PRAM, NRAM, SONOS, TRAM, FeRAM and many more. Some use a matrix of magnets to store bits, others use ions within an electrolyte, phase changing materials or various applications of nanotechnology. The dream of some is a universal memory – a single big block of RAM replacing all storage and your main memory.

This one is a way-away yet, but we can certainly expect SSDs to start developing very quickly now and there's a lot of technology filtering down from the server market to come. Desktop drives are turning solid state. And this is a good thing.

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First published in PCFormat Issue 235

Liked this? Then check out Thanks for the memory: the story of storage

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