I taught at Lanier Tech for a while as an adjunct instructor. The
computers there are kept in an electronically frozen (not locked up) state
so the students cannot make any changes to them. If something is messed
up, you just reboot. Therefore, they cannot store any permanent work on
them. For that, they use memory sticks. I always encouraged them never to
rely on a memory stick as their only storage for their work. I've seen a
few times when the data just vanished or was corrupted. The cells in a
flash memory device have a limited number of read / write cycles that they
will tolerate. After that, they fail to function. If, for example, you
set a memory stick to be your temp swap file, you'd probably burn it up
quickly.
From Wikipedia -->
http://en.wikipedia.org/wiki/Flash_memory
The write endurance of SLC Floating Gate NOR flash is typically equal or
greater than that of NAND flash, while MLC NOR & NAND Flash have similar
Endurance capabilities. Example Endurance cycle ratings listed in
datasheets for NAND and NOR Flash are provided.
* SLC NAND Flash is typically rated at about 100K cycles (Samsung
OneNAND KFW4G16Q2M)
* MLC NAND Flash is typically rated at about 5K-10K cycles (Samsung
K9G8G08U0M)
* SLC Floating Gate NOR Flash has typical Endurance rating of 100K to
1,000K cycles (Numonyx M58BW 100K; Spansion S29CD016J 1000K)
* MLC Floating Gate NOR Flash has typical Endurance rating of 100K
cycles (Numonyx J3 Flash)
<--
Some flash memory, usually more expensive ones, use wear leveling
techniques to spread the writes over lots of cells and improve the average
life of the device. Since you never know which cells / sectors you're
really writing to, I don't know if there is even a way to test a memory
stick to verify it's integrity the way you could with a HDD. Some also use
spare sectors to write to when parts of the unit fail. There are also two
fundamental cell types, SLC and MLC. This is getting beyond my level of
expertise, but based on what I've read and heard, SLC stores one bit of
information in each cell by storing one level of charge. MLC stores
multiple bits of information per cell by storing various levels of
charge. They can be also configured as NAND or NOR. MLC is cheaper and
less reliable. SLC is more expensive and more reliable. So, the really
cheap memory stick you get at the store may be the least reliable of
all. Note that the MLC NAND item above will only tolerate 5K - 10K cycles,
versus 100K - 1000K cycles for the best ones.
So, as Wolf said, life expectancy is questionable, but what's worse, it
varies by the construction of the device, and the usage pattern. Depending
on the application, device life could be much less than 5 years. I do
believe reading the data is non destructive to the device, but I'm not sure.
For what it's worth, I just had a personal experience which may be related
to a flash memory failure. I have a portable MP3 player that I listen to
technical podcasts on. I have hundreds of files on it. I listen to them,
then erase them, and load new ones. I recently was listening to a podcast,
and all of a sudden, it began playing audio from another unrelated podcast,
but the screen said it was still playing the same file. I've confirmed
that the original source file on my computer is valid, so I suspect data
corruption in the flash file. If this were a HDD, I'd use Spinrite to do a
read / write integrity test on every sector. I don't even know if that's
possible on a flash memory card. I guess I'll just erase the file and
reload it.
By the way, in my opinion, the jury is still out on the longevity of SSD
"Hard Drives". I may own one some day, but I still plan to have backups on
spinning platters, for now. If you're storing important data on a memory
stick, I'd certainly want a duplicate elsewhere, and if that duplicate is
on another memory stick, I'd be inclined to test the files periodically and
refresh them, money permitting of course.
Steve Gibson has periodically talked about flash memory on the Security Now
podcast. You might try this search on Google:
"flash memory" site:grc.com
PS - My parents periodically take their photo memory card to Walmart, plug
it into the kiosk, and have a Photo CD made. I have no idea what that
costs. Also, something like Jungledisk or Carbonite might be a great way
to make sure those photos are backed up online. I use Jungledisk. The
cost is $ 0.15 / GB / Mo. for storage. When you send or receive data,
there is a bandwidth fee of something like $ 0.18 / GB, and a $ 3 / Mo.
maintenance fee I believe. If most of your files are archival and don't
change much, the cost is not too high. There is a premium option which
only uploads the changed parts of updated files for an extra $ 1 / mo, I
believe. I don't know about the cost structure of Carbonite.
Sincerely,
Ron
At 10/4/2010 06:48 AM -0400, Wolf wrote:
>Even the best CDR-W have about a 2-year life expectancy
>Paper is by far the most time-resistant media for photos.
>Ansel Adams Photos still exist. (They always looked that weird)
>
>Do you want to start talking about the relative friability of media?
>flash memory has about a max life of 5 years unless the stick or
>SHD is powered up at regular intervals. (I am not sure of the interval)
>
>-Wolf
>
>
>-----Original Message-----
>From: Paul Cartwright
><<mailto:Paul%20Cartwright%20%3cale at pcartwright.com%3e>ale at pcartwright.com>
>Reply-to: Atlanta Linux Enthusiasts - Yes! We run Linux! <ale at ale.org>
>To: Atlanta Linux Enthusiasts - Yes! We run Linux!
><<mailto:Atlanta%20Linux%20Enthusiasts%20-%20Yes!%20We%20run%20Linux!%20%3cale at ale.org%3e>ale at ale.org>
>Subject: [ale] OT- Re: Cd-r life
>Date: Sun, 3 Oct 2010 06:46:52 -0400
>
>
>
>On Sat October 2 2010, Ron Frazier wrote:
> > TDK had a similar product at one time, but I couldn't find it on their
> > website now. Here's the link to their storage media website. Look for the
> > word archival in the name, but be sure to check the specs. Some discs are
> > just a heavy duty scratch resistant standard discs.
> >
> >
> <http://www.tdkperformance.com/en-us/Storage-Media/>http://www.tdkperformance.com/en-us/Storage-Media/
>ok, since we are now talking photos & not linux, it becomes OT:)
>
>the problem with the photoarchival TDK CDs is, it now takes me 2 DVDs to
>store
>my photos, and that size grows almost daily:) I now use at least 1 USB stick
>to store photos on. As soon as I get A JOB, I will get a bigger USB stick,
>and eventually multiple sticks, just for my photos..
--------------------------
(PS - If you email me and don't get a quick response, you might want to
call on the phone. I get about 300 emails per day from alternate energy
mailing lists and such. I don't always see new messages very quickly.)
Ron Frazier
770-205-9422 (O) Leave a message.
linuxdude AT c3energy.com
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