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From: H.K. Kingston-Smith on 28 Nov 2007 14:38
I am using an 8 GB USB stick for my backups. The approach that I
follow consists of using rsync every other day in order to keep the
contents of the stuff in the backup in sync with the original stuff. My
question is, How long can I expect the USB stick to last?

I understand that a USB stick can be written to only so many
times, but I don't know how a write operation is to be accounted for in
this context. With my approach, the stick is written to intensively the
first time, when it is empty; however, every subsequent backup operation
will only copy the files/directories that have been changed in, or added
to, (and remove files/directories that have been removed from) the
original since the last backup operation.

Is this a sensible approach, or will it render my USB useless in
no time?

From: General Schvantzkopf on 28 Nov 2007 15:27
On Wed, 28 Nov 2007 19:38:17 +0000, H.K. Kingston-Smith wrote:

> I am using an 8 GB USB stick for my backups. The approach that I follow
> consists of using rsync every other day in order to keep the contents of
> the stuff in the backup in sync with the original stuff. My question is,
> How long can I expect the USB stick to last?
>
> I understand that a USB stick can be written to only so many
> times, but I don't know how a write operation is to be accounted for in
> this context. With my approach, the stick is written to intensively the
> first time, when it is empty; however, every subsequent backup operation
> will only copy the files/directories that have been changed in, or added
> to, (and remove files/directories that have been removed from) the
> original since the last backup operation.
>
> Is this a sensible approach, or will it render my USB useless in
> no time?

A FLASH RAM is good for about 10000 cycles so if you are only doing a
write every few days you shouldn't have a problem.
From: Janaka on 28 Nov 2007 21:44
On Nov 29, 6:38 am, "H.K. Kingston-Smith" <HK...(a)yahoo.com> wrote:
> I am using an 8 GB USB stick for my backups. The approach that I
> follow consists of using rsync every other day in order to keep the
> contents of the stuff in the backup in sync with the original stuff. My
> question is, How long can I expect the USB stick to last?
>
> I understand that a USB stick can be written to only so many
> times, but I don't know how a write operation is to be accounted for in
> this context. With my approach, the stick is written to intensively the
> first time, when it is empty; however, every subsequent backup operation
> will only copy the files/directories that have been changed in, or added
> to, (and remove files/directories that have been removed from) the
> original since the last backup operation.
>
> Is this a sensible approach, or will it render my USB useless in
> no time?

Most Flash chips have 100,000 write cycles. Some of the good chips
have 1,000,000 ; but you wouldn't be able to tell whether your flash
stick has a good chip without opening it.
As far as the storage goes, some dedicated file systems (such as
JFFS2) are excellent at how they handle flash writes. They tend to
share the burden of flash writes on all its sectors/segments (Eg: if
you re-write a single file multiple times, it gets moved to different
areas in flash [in a nutshell]). So use such a file system if
possible.
Also note that the 100,000 write cycles are a MTBF value. It may last
longer. Also every flash erase is a flash write. It writes usually
0xFF to the memory location. And every storage is a clearing of bits
from that 0xFF to what you want. Therefor I think every erase/write
is actually two writes (but don't quote me on that!).
From: Peter Chant on 29 Nov 2007 15:42
Janaka wrote:


> 0xFF to the memory location. And every storage is a clearing of bits
> from that 0xFF to what you want. Therefor I think every erase/write
> is actually two writes (but don't quote me on that!).

I seem to recall that writes are fine, it is the erases that are the
problem. Unfortunately changing things involves an erase.

--
http://www.petezilla.co.uk
From: Arno Wagner on 4 Dec 2007 17:39
Previously H.K. Kingston-Smith <HKK-S(a)yahoo.com> wrote:
> I am using an 8 GB USB stick for my backups. The approach that I
> follow consists of using rsync every other day in order to keep the
> contents of the stuff in the backup in sync with the original stuff. My
> question is, How long can I expect the USB stick to last?

> I understand that a USB stick can be written to only so many
> times, but I don't know how a write operation is to be accounted for in
> this context. With my approach, the stick is written to intensively the
> first time, when it is empty; however, every subsequent backup operation
> will only copy the files/directories that have been changed in, or added
> to, (and remove files/directories that have been removed from) the
> original since the last backup operation.

> Is this a sensible approach, or will it render my USB useless in
> no time?

Very long, if it is a quality stick. While individual cells
only last 10.000-1.000.000 cycles (depending on technolology),
wear-leveling makes modern flash sticks very hard to destroy.

One thing you should do nonetheless is verify your backups.
This will also provide early warning in case sectors do degrade.
If rsync does read all data, then this is enough.l Othervise you
may want to add an explicit verify pass.

Another thing you should definitely do is get at least two
more medua and do rotating backups. It is far to easy to destroy
your backup and find out at the same time that the original data
was corrupt.

Arno
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