Feeds

Resistive Ram cache to make Flash fly, say boffins

Wham, bam, thank you, RRam

Internet Security Threat Report 2014

Cache in hand

In the other direction, the RRam cache is large enough so that data can be held there until there's a sufficient quantity of it to write it out to Flash efficiently.

So quite apart from allowing the drive to appear to operate at RRam rather than Flash speeds, this has the added benefit of organising the data to minimise and possibly eliminate the small, random writes, and the data fragmentation they engender, which are the bugbear of Flash performance and reduce chips' longevity.

The design of Flash chips makes it necessary to write a whole chunk of data - called a Page - of up to 4KB in size even if only a few bytes need to be changed. This is because Flash Pages need to be erased before they can be written to. Worse, Flash has to be erased a Block at a time, and a Block is a much larger amount of memory than a Page, 16KB or bigger. Each erase and write operation gobbles up power.

Caching allows that entire 4KB write to comprise new data. So while 4KB still needs to be written, it does so once rather than every time one part of the page changes.

The Chuo University university designed such a hybrid SSD using 256GB of Flash and 1GB of RRam. The team didn't build such a device, but simulations yielded an 11x increase in write performance - 4.2MB/s for the Flash alone, rising to 46MB/s with the RRam cache in place - and a 79 per cent reduction in the energy consumed for all these writes: 0.12J/MB down to 0.024J/MB.

The team reckon that with smarter, 3D chip construction, connecting the controller, RRam and Flash chips with lines that run through each part - called Through Silicon Vias - the energy saving is even greater, with consumption falling to 0.008J/MB.

Reduced writing means increased longevity: the Flash chips in the Hybrid SSD would last, the team reckons, more than seven times as long as those in a Flash-only SSD. Hybrid drives will cost more, of course, but as long as the extra is less than the price of seven SSDs, that's good news for data centres bulk-buying solid-state drives.

A more logical approach would be to migrate to RRam SSDs, but these are some way off. RRam chips aren't expected to go into mass production until 2014. It will be some years more before they reach today's NAND Flash chip prices.

And the Chuo team's approach applies equally to SSDs with a cache of regular Ram. The downside here, of course, is that Ram loses its data when the power is cut, so the drive needs to be able to hold sufficient energy to write the contents of the Ram cache to Flash as soon as a power cut is detected.

While the Japanese team waits for RRam to become more readily available, companies like Sandforce and Indilinx are building better Flash controllers more able to work around NAND's limitations. But RRam's speed advantage will be hard to beat. ®

Beginner's guide to SSL certificates

More from The Register

next story
NSA SOURCE CODE LEAK: Information slurp tools to appear online
Now you can run your own intelligence agency
Azure TITSUP caused by INFINITE LOOP
Fat fingered geo-block kept Aussies in the dark
Yahoo! blames! MONSTER! email! OUTAGE! on! CUT! CABLE! bungle!
Weekend woe for BT as telco struggles to restore service
Cloud unicorns are extinct so DiData cloud mess was YOUR fault
Applications need to be built to handle TITSUP incidents
Stop the IoT revolution! We need to figure out packet sizes first
Researchers test 802.15.4 and find we know nuh-think! about large scale sensor network ops
Turnbull should spare us all airline-magazine-grade cloud hype
Box-hugger is not a dirty word, Minister. Box-huggers make the cloud WORK
SanDisk vows: We'll have a 16TB SSD WHOPPER by 2016
Flash WORM has a serious use for archived photos and videos
Astro-boffins start opening universe simulation data
Got a supercomputer? Want to simulate a universe? Here you go
Microsoft adds video offering to Office 365. Oh NOES, you'll need Adobe Flash
Lovely presentations... but not on your Flash-hating mobe
prev story

Whitepapers

10 ways wire data helps conquer IT complexity
IT teams can automatically detect problems across the IT environment, spot data theft, select unique pieces of transaction payloads to send to a data source, and more.
A strategic approach to identity relationship management
ForgeRock commissioned Forrester to evaluate companies’ IAM practices and requirements when it comes to customer-facing scenarios versus employee-facing ones.
10 threats to successful enterprise endpoint backup
10 threats to a successful backup including issues with BYOD, slow backups and ineffective security.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?
Website security in corporate America
Find out how you rank among other IT managers testing your website's vulnerabilities.