On Sat, 21 Jul 2012 18:10:57 -0400, "Soundhaspriority"
wrote:
:
:
: "Mxsmanic" wrote in message
: news
: Just out of curiosity, have you ever actually experienced a memory card
: failure due to simple wear and tear?
:
: I know that flash memory allows for only a limited number of write cycles,
: but
: I'm curious as to how often this limit has actually affected people in
: real
: life.
:
: I've never experienced a memory-card failure of any kind [knocking on
: wood],
: and hopefully I never will, although a simple inability to write to the
: card
: would probably be less of a disaster than an inability to read what's
: written
: (apparently wear and tear only impedes writing, but reading still works).
: I
: always have several cards with me at least, and I try to cycle through
: them to
: even out the wear and tear. I've been lucky so far.
:
: Memory cards use NAND flash, which is a very strange medium. When NAND is
: used in a memory card, it is written only in large blocks; individual
: addressing is not possible in this application. The illusion that a single
: address can be rewritten is provided by rewriting the block.
:
: NAND cells are inherently unreliable. When a block is written, there almost
: CERTAINLY will be errors. The user does not see the errors because the block
: is written using a very robust error correcting code.
:
: Nota bene: flash is an unreliable physical device, with clever engineering
: used to provide the appearance of a reliable end user device.
:
: NAND is pattern sensitive to READ disturbance. When cells nearby are read
: [sic], it actually disturbs the reliability of the cell, which should, in
: theory, be rewritten at intervals.
:
: Consumer NAND flash now uses MLC (multi-level-cell) architecture, which has
: a much shorter lifetime than what used to be the gold-standard, SLC (single
: level cell.) SLC is now available only for enterprise apps. The short cell
: lifetime is allegedly disguised by wear-leveling algorithms, but when the
: block error rate exceeds the ECC capability, and READ disturbances
: occur...who knows?
:
: All this might be too complicated for the microcontroller embedded in a
: flash device to handle reliably. With flash, clever engineering created a
: problem that isn't simple. But the consumer needs flash. Providing it at a
: price the consumer is prepared to pay has resulted in a product that doesn't
: fail predictably. Predictable wear out has been replaced by catastrophic
: failure, as the rule, rather than the exception.
:
: In some cases, a memory requirement can be addressed by either flash or hard
: drive. In the case of a Sound Devices 744T, I chose to stick with the hard
: drive. My personal "feeling", which I can't substantiate with any hard info,
: is that some hard drives, selected for both make and particular model, and
: handled and mounted to avoid mechanical shock, are more reliable than flash
: alternatives.
Well, that's an entertaining thought, but hard drives in CF format have been
tried. And my recollection (though I never owned one) is that they were
expensive and quite fragile.
: Bob Morein
: (310) 237-6511
I will say this: you've got the nerve to use your real name and even your
phone number. Some of the naysayers who have already lined up to tell you off
are far too gutless to do that. ;^)
Bob