Hi Folks,
This morning's Guardian "Technology" section has an item about the possible replacement of the classic HDD by flash-memory modules. See:
http://technology.guardian.co.uk/weekly/story/0,,1856508,00.html
While reading the article (mostly about cost comparisons), I was wondering about whether the data stored on a flash module would be as solidly stored as on a HDD. Finally, there was a brief discussion of the issue:
"But besides cost, there are other obstacles for Flash memory replacing hard drives. Flash memory is typically guaranteed for around 1m read/write cycles, which sounds a lot, but in the context of the working life of a PC (which is continually writing, erasing or rewriting data) is not. So designers have to use techniques known as wear-levelling to shift data around the Flash memory block to reduce the risk of data error. "We can design around the problem," says Walsh."
I was also wondering about how long data would "stay in place" over time anyway. Does the "bit-state" of an element on a flash module tend to "diffuse" away over time?
Admittedly I have never experienced data corruption on a flash drive (though the number of read/writes to such that I've made is far from the millions); aqnd I've certainly had problems with hard drives! (But then I do hammer these).
Any views?
There's also an interesting insight into XP and Vista. Booting XP from a flash would be 25%-50% faster than from a HDD. And, it says, "Vista is about five times bigger than XP, and what comes along with that large size is a speed issue, even with faster CPUs. We've been working with Microsoft on ways to speed up booting and application loading by complementing the hard drive with Flash."
Hmmm
Best wishes to all, Ted.
-------------------------------------------------------------------- E-Mail: (Ted Harding) Ted.Harding@nessie.mcc.ac.uk Fax-to-email: +44 (0)870 094 0861 Date: 24-Aug-06 Time: 10:54:16 ------------------------------ XFMail ------------------------------
On Thu, 2006-08-24 at 10:54 +0100, Ted.Harding@nessie.mcc.ac.uk wrote:
I was also wondering about how long data would "stay in place" over time anyway. Does the "bit-state" of an element on a flash module tend to "diffuse" away over time?
I am not sure what the data persistence is of Flash memory but I would say that it should at the very least be better than a hard drive. The maximum write thing is improving all the time, which in combination with a wear levelling algorithm should mean that flash has the potential to be more reliable.
The one problem is that at the moment (excepting single bit failures) flash memory failures tend to be quite unpredictable. As Barry is currently finding out many (if not most) hard drive failures are predictable if you are monitoring the health status of the drive. This is because most hard drive failures are mechanical which have a tendency to degrade into a failure condition fairly slowly.
What I fully expect to see very soon are hybrid devices with enough on board intelligence to move data between flash and disk based storage based on access patterns. This is better than the vista approach because it is not using bus bandwidth. It will also (at least initially) be more accessible as I think it will be a long time before Flash can hit the cost per megabyte at the storage densities we are now used to.
We've been working with Microsoft on ways to speed up booting and application loading by complementing the hard drive with Flash."
This is already in the Vista betas, It can use a flash key drive as a sort of swap space/disk buffer. It's all done in a pretty clever way where unplugging the flash disk won't break anything and it evaluates each keydrive to determine whether it is fast enough to actually provide a benefit.
On Thu, Aug 24, 2006 at 10:31:09PM +0100, Wayne Stallwood wrote:
What I fully expect to see very soon are hybrid devices with enough on board intelligence to move data between flash and disk based storage based on access patterns. This is better than the vista approach because it is not using bus bandwidth. It will also (at least initially) be more accessible as I think it will be a long time before Flash can hit the cost per megabyte at the storage densities we are now used to.
This is part of the new Vista technology (called readydrive I believe?) which is a joint venture between Samsung and Microsoft so that laptop hard disks will have a cache of around 256 megs of flash on them so that resuming from hibernate can be done more quickly and it will allow a laptops hard disk to spend more time with the disk spun down thus saving power. It could also mean booting at power on with a larger cache is reduced as everything will be in flash and that the disk is less likely to be damaged when you drop your laptop as the disk is more likely to be spun down at any given moment in time.
In the older days of computing (I believe during the 80's) a common way to speed up hard disk was to have a megabyte or two of ram on the disks controller (especially used in database applications) which was battery backed up with a couple of AA batteries. In the event of a power a failure the disk would always be in a consistent state too (well, unless the batteries went flat which would take a couple of weeks) as the cached writes on the controller would know exactly what had actually been written out to disk. I'm sort of going on memory with this though as this was all related to me by someone I know who administered quite a bit of Sun kit during the 80's.
Thanks Adam
On Thu, 2006-08-24 at 23:13 +0100, Adam Bower wrote:
This is part of the new Vista technology (called readydrive I believe?)
Pah why does this have to be a "Vista" technology, it should be done at a hardware level dammit. I guess they want the OS to decide what bits are worth marking as being better on the flash (Like the hibernate image) But then even that is flawed because if you extend your system memory over the size of the flash you are stuffed surely. Lets face it given Vista's minimum and recommended requirements nobody is going to be using this with 256MB RAM.
In the older days of computing (I believe during the 80's) a common way to speed up hard disk was to have a megabyte or two of ram on the disks controller (especially used in database applications) which was battery backed up with a couple of AA batteries.
This is still very common on SCSI RAID controllers, if you power up any Compaq server with the 5i Storageworks controller that has been left off for a while it will warn you that it is running in degraded performance until it's batteries are fully charged.
On Fri, Aug 25, 2006 at 01:03:28AM +0100, Wayne Stallwood wrote:
On Thu, 2006-08-24 at 23:13 +0100, Adam Bower wrote:
This is part of the new Vista technology (called readydrive I believe?)
Pah why does this have to be a "Vista" technology, it should be done at a hardware level dammit. I guess they want the OS to decide what bits are worth marking as being better on the flash (Like the hibernate image) But then even that is flawed because if you extend your system memory over the size of the flash you are stuffed surely. Lets face it given Vista's minimum and recommended requirements nobody is going to be using this with 256MB RAM.
It will be part of ATA8 specs too I believe. Just that Microsoft are leading the way. I'd guess that the disk just looks the same as any other disk to the controller but when combined with magic drivers it will be more "clever". I don't see that just because your system image is more than 256 megs it won't fit on the flash as being sufficiently flawed, as first off you can compress the image onto the flash and if it's enough to get your kernel and drivers on there it will make the system restore fast enough that all the other applications will just be sitting in what will be effectively swap on the main disk (if you engineer this in a sufficiently clever way the restore image on the disk will be exactly swap so you don't actually have to do anything to read from it). When you select your first application it will get swapped back in which will still be faster than loading _everything_ from the disk.
You also have to consider that even when you've just recovered from a hibernate state one thing that takes the most time is the machine reconnecting to networks and working out where it is and spending a few seconds working out where it's going. Of course, if the technology works then I can see drives with at least 1 or 2 gigs of flash appearing very soon.
Thanks Adam
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Adam Bower -
Ted.Harding＠nessie.mcc.ac.uk -
Wayne Stallwood