On Thu, 21 Jun 2007 02:48:50 -0700, Rui Maciel wrote:

> After having a few nasty surprises with some CDs where I stored
> important data, I've started searching for a good way to store data
> that didn't lead to data corruption in the span of a year or two.

Makes me wonder how you stored the CDs. At any rate, I'm convinced that
the best solution is multiple archives - spread around. I archive my
photos by: storing them a couple of different places on hard disks on two
or three different computers and backing up to CD. I also don't usually
erase the memory cards until they are full - in my case that takes a
while. I've had photos stored on a CF card for about three years with no
data loss.

>
> The first thing that crossed my mind was flash memory cards. They are
> starting to get affordable, their capacity ranges from a couple of MB
> to 8GB and their size makes them pretty handy. Yet, I haven't found a
> single shred of information regarding data longevity. There is plenty
> of information regarding the typical number of write cycles that a
> typical flash memory card can handle but I couldn't find a single
> piece of information about how long it can be expected that the data
> remains stored and retrievable from a flash card.
>
> So, can anyone help me? How long can I expect data to remain stored in
> a flash memory card?
>
>
> Thanks in advance
> Rui Maciel

On Jun 21, 3:30 pm, ray wrote:

> Makes me wonder how you stored the CDs.

I stored the CDs in their jewel case which then were kept in their
original 10-CD pack cardboard box. That box was kept in an office
shelf. They weren't lying around or kept in any damped environment.
Just you regular 90%-ish humidity level, 20 to 30 degrees centigrade
office.


> At any rate, I'm convinced that
> the best solution is multiple archives - spread around. I archive my
> photos by: storing them a couple of different places on hard disks on two
> or three different computers and backing up to CD.

It seems to be a reasonable solution. Yet, as I've experienced quite
some corruption problems with CDs, I have to keep them out of
consideration for fears of having to live through the same situation
as before.

> I also don't usually
> erase the memory cards until they are full - in my case that takes a
> while. I've had photos stored on a CF card for about three years with no
> data loss.

That sounds promising. But is there any objective information about
flash memory durability through time?


Thanks for the help
Rui Maciel

>> Makes me wonder how you stored the CDs.
>
> I stored the CDs in their jewel case which then were kept in their
> original 10-CD pack cardboard box. That box was kept in an office shelf.
> They weren't lying around or kept in any damped environment. Just you
> regular 90%-ish humidity level, 20 to 30 degrees centigrade office.

CDs seem to be sensitive to UV light. They're supposed to last 18
months. Although I'm sure some last longer than that, and shorter than
that. I personally don't trust my backups a media type that has a 25% or
higher failure rate at creation time.

One would think that solid state storage devices like flash drives would
last a while. But as far as value ($$$ per GB) hard disks are better.
$1 per GB or less versus $50 per GB. If portability and size are issues,
then I guess it's worth the expense. Personally I haven't found a need
to go that route myself. I can ftp data on/off my laptop with a 60GB
hard drive at no extra costs. A laptop that costs as much or less than
the largest of those sticks (8GB/16GB).

Redundancy is the only reliable route with needed backups. Multiple
copies in case one or more gets messed up. One local and one off site at
a minimum. Nothing like a good fire or terrorist attack to whipe out 20
plus years of infrastructure.

On Thu, 21 Jun 2007 16:18:54 +0000, Shadow_7 wrote:

>>> Makes me wonder how you stored the CDs.
>>
>> I stored the CDs in their jewel case which then were kept in their
>> original 10-CD pack cardboard box. That box was kept in an office shelf.
>> They weren't lying around or kept in any damped environment. Just you
>> regular 90%-ish humidity level, 20 to 30 degrees centigrade office.
>
> CDs seem to be sensitive to UV light. They're supposed to last 18
> months. Although I'm sure some last longer than that, and shorter than
> that. I personally don't trust my backups a media type that has a 25% or
> higher failure rate at creation time.
>
> One would think that solid state storage devices like flash drives would
> last a while. But as far as value ($$$ per GB) hard disks are better.
> $1 per GB or less versus $50 per GB. If portability and size are issues,
> then I guess it's worth the expense. Personally I haven't found a need
> to go that route myself. I can ftp data on/off my laptop with a 60GB
> hard drive at no extra costs. A laptop that costs as much or less than
> the largest of those sticks (8GB/16GB).

I have to question your numbers. First, 250gb and larger hard drives are
routinely under $100 now. Second, CDs and DVDs come for around $20 per
stack of 25 to 50 which puts them in the $0.50-$1.00 or lower range - not
really that much difference; and 2gb flash drives are about $20 now,
making their cost significantly less than $10/gb and even less on larger
sizes.

I also back my stuff up to an external USB drive which should have a
fairly long life since I don't use it that much, but enough to keep it
'limber'.


>
> Redundancy is the only reliable route with needed backups. Multiple
> copies in case one or more gets messed up. One local and one off site at
> a minimum. Nothing like a good fire or terrorist attack to whipe out 20
> plus years of infrastructure.

Rui Maciel wrote:
>
> So, can anyone help me? How long can I expect data to remain stored in
> a flash memory card?
>

Manufacturer's data sheets usually claim 10 years.
Bits will rot one-by-one and NAND-FLASH has ECC codes
to compensate.

They do wear out in repeated erase-reprogram cycles
(in the order of thousands). For long term storage,
you should be OK if you refresh (erase & rewrite) the
contents once every five years or so.

SD cards have a built-in controller which will replace
defective blocks with reserve space on such occasions.

Kind regards,

Iwo