how long will a flashdisk last?


Sandisk Cruzer Profile fingerprint reader

Image via Wikipedia

It took 90 million writes for the drive to die

based on this blogpost, it can be concurred that when your flashdisk failed, you won’t lost the data in it. rather that you won’t be able to write anything in that drive ever again. but you can still read the data as the flashdisk had become in read-only mode.

A flash drive doesn’t carry any sort of charge, static or otherwise. It’s not water that kills electronics though, but when water closes electrical pathways, that would otherwise be isolated, and causes a short circuit. For such a simple device like a flash drive, if you get it wet, just make sure to dry it out well before you power it up next

The lifetime of flashdrive is measured in program/erase cycles. Most modern ones are good for up to about 1,000,000 cycles, depending on the technology used (some are closer to 100K). Damaged memory blocks can be dynamically rewritten.

From wiki:

“Another limitation is that flash memory has a finite number of program-erase cycles (typically written as P/E cycles). Most commercially available flash products are guaranteed to withstand around 100,000 P/E cycles, before the wear begins to deteriorate the integrity of the storage.[7] Micron Technology and Sun Microsystems announced an SLC flash memory chip rated for 1,000,000 P/E cycles on December 17, 2008.[8]”

The guaranteed cycle count may apply only to block zero (as is the case with TSOP NAND parts), or to all blocks (as in NOR). This effect is partially offset in some chip firmware or file system drivers by counting the writes and dynamically remapping blocks in order to spread write operations between sectors; this technique is called wear leveling. Another approach is to perform write verification and remapping to spare sectors in case of write failure, a technique called Bad Block Management (BBM).

For portable consumer devices, these wearout management techniques typically extend the life of the flash memory beyond the life of the device itself, and some data loss may be acceptable in these applications. For high reliability data storage, however, it is not advisable to use flash memory that would have to go through a large number of programming cycles. This limitation is meaningless for ‘read-only’ applications such as thin clients and routers, which are only programmed once or at most a few times during their lifetimes.”

also In the article, the author creates a small one-block file, then fills up the whole filesystem so that, he reasons, re-writing the small file will only re-write the block is sits on. The problem with that approach is that wear-levelling algorithms and hardware have no sense of file systems. They can’t possibly try to understand them, and especially not all of them. They don’t know how full your FS is; all they know is how often a block has been written to.

In this test, the wear-levelling hardware/firmware just knew that one logical block was being written to often. So what is did was to re-located that block to a different physical one, as often as it judged necessary. 90 million write is very poor reliability. It’s hard to tell how many physical writes that was without knowing how the flash was partitionned, the largest configuration I read about was 32kb/block, so that still amounted to over 31 billion writes.

It is also worth noting that even if you didn’t use the flashdisk, it would eventually lose charge and the data would be lost, though this is likely to take at least 10 years for it to happen.

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