It has been suggested that flash drives be used for long term storage of critical data. They would be written to once and lock in the safe.
I understand that R/W is limited by the number of times it is accessed, but what about long term, unaccessed storage?
How long is long-term? Look ye here.
That article is a puzzlement. It refers to progressive fragmentation on flash memory as a problem. Now, I am quite familiar with the concept on hard or floppy drives, where file allocations are broken up as needed to fill empty space that may be all over the map on the drive. This causes excessive head movement, and since head movement is one of the slower aspects of reading a disk, it not only wears out the physical mechanism but makes for slower reads.
But a flash drive has no moving parts. It reads data by random access. There is no penalty to accessing addresses sequentially as 0000, 0001, 0002, 0003… or randomly like 0000, FEAD, 0043, 98FF… Data is addressed by a pointer, which has no physical movement and no bias towards low or high numbers.
So why would fragmentation of a flash memory be a problem? I would think that defragging would be a worse idea, since it would add to the total number of reads and decrease the remaining number available from a finite value (unlike RAM, which is considered to be infinite).
I would agree.
The question, though, is what happens when a flash drive has been locked up in the safe for three years and someone wants to see CP’s time sheet from three years ago.
I don’t know the life expectancy of flash, although 3 years doesn’t seem like too long a time to expect readability. But if long-term data storage is the goal, I would suggest storing duplicate copies of the data on as many different kinds of media as you can – CD/DVDs, flash, maybe even floppies if it fits – and be prepared to migrate to any new medium that comes along. But don’t discard the originals!
Someone who knows more about flash will surely come along, but it occurs to me that “refreshing” the data periodically might make it last longer. This is true for EPROMs, which reportedly can get weak and/or lose random bits over several years. Refreshing a flash drive could be done by reading and verifying all data, then re-writing it to the same drive.
And don’t forget that ink on paper is the ultimate storage medium in many ways. It is more likely to be readable 100 years from now than anything else we have yet invented.
I work in the computer biz and I would never bet long term storage on flash devices at this point. Need something to move a large file to another machine or across town, fine, but not as a true backup solution. True archival storage is a huge topic, things like converting data to CSV files or something to make sure future software can read it are issues worth considering. Just for a backup solution, RAID equipped machines holding copies of the files are tough to beat.
Ain’t it though. Our mechanical drawing professor gave us an illustration of what can happen to records in storage.
A guy where he once worked had some vellum drawing originals in his desk along with a plastic triangle. Apparently he had them in the drawer for a couple of years. One day he needed a drawing and went to take it out. On his doing so it crumbled and fell apart. It turned out that the plastic in the triangle had outgassed over the period and since the drawer was seldom opened the gas had embrittled the vellum.
The incident caused quite a stir since the vellum was the original drawing for the part and it led to an intensive search in the files of original drawings to purge them of plastic or other material that could outgas.
I’m not an expert, but I have heard that memory based on magnetic domains, as with flash drives, is fragile. CDs or DVDs are theoretically less so, but I have also heard of oxidation issues related to the exterior coatings of them.
Does this mean I shouldn’t use a flash as backup for my Word files? I backup the entire thing about once a week or two… so no files are just sitting on there forever without be written over.
Short term, great. Long term, [Paul Reiser]maybe not so much.[/Paul Reiser]
There are multiple reasons that fragmentation is a problem for flash. The less likely reason is that usually it’s the operating system that has to handle the logical-to-physical translation when accessing the flash. Depending on how the hardware access to flash is arranged, the OS/driver might wind up babysitting each block instead of a range of blocks because everything is out of order. The more likely reason is that the actual Flash chip supports burst mode that gets a block # and a range instead of each consecutive block number. Another aspect is that logical blocks are originally consecutive but as bad blocks are found and marked everything gets out of order and sequential reads might not be possible.
Flash drives use stored electrical charges, not magnetic domains. Over long periods of time, the electrical charges can leak away.
Unless you get a power spike that damages all your drives, or you accidently do a format, or your building and server burns down, or a virus deletes all the files, etcetera, etcetera. I wouldn’t trust my data to just RAID, there are just too many ways that RAID can fail.