Re: off-site backup
On 10/16/06, dtutty@porchlight.ca <dtutty@porchlight.ca> wrote:
Just a reminder,
reply to the list. I'm not sure which list you read it on, so I sent it
to both.
On Mon, Oct 16, 2006 at 11:06:22AM -0600, Cedar Cox wrote:
> >It seems that USB sticks/flash-drives are far more rugged than anything
> >other than paper. What have you found?
>
> Flash memory does have limited write cycles. This is probably more an
> issue for people who carry a Linux distro on their stick than you for
> backup, but it is an item to consider.
Does anyone know what the limit is? 10 years at monthy is 120 cycles;
10 years at weekly is 520 cycles, 10 years at daily is 3,650.
According to Wikipedia's page on Flash Memory, typical products are
"guaranteed to withstand 1 million programming cycles," which takes
place in a block-by-block fashion. (I'm not sure how big the blocks
are.)
http://en.wikipedia.org/wiki/Wear_levelling
The troublesome part is that filesystem metadata tends to get
rewritten really frequently. Thus directory structures will get
hammered pretty badly with FAT/ext2/such.
Does the cycle limit apply to the whole device or does a section get
worn out and the capacity just shrink? E.g. if I have my /etc/
directory copied to it and one file in /etc/ changes, does changing that
one file reduce the lifespan of the drive as a whole?
If you can use some form of "wear levelling," then no. Apparently
JFFS2 is designed to do this sort of thing...
http://en.wikipedia.org/wiki/JFFS2
I don't know how a memory chip gets translated into a 'drive'. Is it
like a HDD with spare sectors?
The usual way it's handled is to pretend it's a SCSI drive...
--
http://www3.sympatico.ca/cbbrowne/linux.html
Oddly enough, this is completely standard behaviour for shells. This
is a roundabout way of saying `don't use combined chains of `&&'s and
`||'s unless you think Gödel's theorem is for sissies'.
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