Re: NAND flash misery

Didi wrote:
Dombo wrote:
Didi schreef:
Vladimir Vassilevsky wrote:
...

I was under impression that flash is more reliable then HDD; now I see
that it is not so. Do you know how reliable are the IDE flash drives?

Vladimir,
if flash were a viable and reliable replacement for HDDs this would
have
happened for years by now, the costs would have gone down. They are
not, and given their limited number of write cycles they are bound to
stay out of the way of normal disks (which have achieved an amazing
level of performance).
When the platter densities of (mechanical) HDD's went up at a certain
point manufactures of HDD's had to resort to error correction schemes to
obtain reliable operation. A modern HDD would be unusable without ECC.
It appears that high density flash is going the same direction.

True, but HDDs don't wear out with writing - and flash does.
This is a major advantage flash does not promise to catch up
with - at least for the time being.


HDDs wear out through use. The lifetime is roughly dependant on the time the hard disk has been powered up, and how much the head is moved. It's thus fairly independent of the size. Flash wears out through erase-write cycles on blocks. So the more blocks you have to spread the wear, the longer the lifetime, and the more you read rather than write, the longer the lifetime. So as flash drives get bigger, they are surpassing HDDs for reliability and lifetime. For common desktop usage, a 32 GB flash disk will probably far outlast a typical hard disk - with 256 GB and bigger flash disks, even high quality hard disks are no longer competitive on reliability and lifetime for real applications.

The big issue is the cost per GB - hard disks are still much much cheaper. A second issue is speed - standard hard disks are significantly faster than standard flash disks. But that will change - flash speeds are easily scaled (just use several devices in parallel) once the price is right.
.

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