Re: [gentoo-user] Gentoo LiveUSB

[Alan McKinnon]

On Friday 11 January 2008, bjlockie@××××××.ca wrote:
> > On Friday 11 January 2008, Anthony E. Caudel wrote:
> >> 2nd question:  I must be dense on this one so someone help me out.
> >> Since a USB stick is seen as a hard drive, why can't I do a
> >> standard install to it?  Is it because until lately they haven't
> >> been large enough?  I'm thinking of using an 8GB one.
> >
> > There's a few reasons:
> >
> > 1. The memory used on those devices has a limited life - about
> > 100,000 writes for the good ones and maybe 10,000 for the bad ones.
> > With a standard install, frequent writes are the norm (think cache
> > and other similar things). This usually ends up at the same spot on
> > the disk, meaning your new install will last about a month if you
> > are lucky. There are ways around this, for instance how a LiveCD
> > does things.

> Does desktop RAM get constantly refreshed while powered and it
> doesn't need to keep any data when not powered?
> Is that the difference?

I'm not sure what you are asking - you're question is poorly framed. So 
I'll answer what I think you are asking.

USB sticks use flash RAM and other non-volatile memory technologies. 
It's not a magnetic disk, it does use transistors but is otherwise 
completely different to desktop RAM. It's also a whole lot slower.

The operating system is almost constantly writing stuff to the disk, and 
not just swap space - many apps cache information and it has to be 
stored somewhere. This is not a problem for magnetic disks as they 
don;t really have a limit on the number of times they can be written 
to. Flash memory does, it stops working after a time. So once you write 
to a memory cell say 50,000 times, it's probably useless. Trouble is, 
you have no way of knowing which cells no longer work, so you have a 
disk with random corruptions. This is usually considered to be a 
VeryBadThing(tm).

alan



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Alan McKinnon
alan dot mckinnon at gmail dot com
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