[vox] Why Linux FS doesn't need defragmenting

[Jeffrey J. Nonken]

On Sat, 19 Aug 2006 23:36:25 -0700
Bill Kendrick <nbs at sonic.net> wrote:

> However, it's currently still much cheaper to squeeze data onto
> magnetic tape than it is to place it in flash memory, so the uses for
> these devices is still mostly limited to digital cameras, MP3 players
> (though note that iPods typically use mini hard drives), PDAs, and
> embedded systems such as routers.  Also, Linux thin client systems
> can be booted off of flash, rather than floppy or hard disk.

Make that "magnetic media" rather than tape specifically.

Flash also has a limit to the number of writes. Magnetic media does
not. Some magnetic media (e.g. tapes, floppies) will wear out because
the heads contact the medium; hard drive heads actually float over the
medium, so as long as the bearings and electronics hold out and the
heads don't crash, you're good to read and write indefinitely.

You can, of course, use RAM instead of flash and eliminate those
problems. But now you're back to the problems of cost and density. In
addition, RAM has the irritating characteristic of losing all its data
as soon as you remove power. Static RAM is much denser than dynamic,
cheaper, and requires less power (I think), but dynamic RAM not only
requires constant power, it also requires frequent refreshes. We're
talking about re-writing every bit of RAM on the order of once per
millisecond.

Bubble Memory (anybody remember that?) was supposed to be the cure-all
for all that. Never got it working.

Core memory can retain its data through power-down. Unfortunately it's
slow, big, and very expensive.

I've heard of some promising technologies revolving around magnetics
(Hall effect or something similar), but so far it's only been noise.
Which isn't to say there isn't something there, but I can't go out and
buy it today.

Believe me, there are a LOT of people who want this. If it were
possible, it would be available. (I mean possible with current
knowledge and technology. I'm not saying it's not possible to do.)

On the other hand, they've gotten REALLY good at packing a lot of data
into a small space, quickly and reliably, with spinning magnetic discs.
And they sell them more cheaply every day. For now I say, use them when
you can, use flash when you have to, and just hang on and wait. There's
always new stuff right around the corner.