Re: CF recording failure


"jason" <absent@xxxxxxxxxxx> wrote in message
news:MPG.23f1929671f1b1f4989827@xxxxxxxxxxxxxxxxxxx
[snip]

So, my questions are these: does NV memory incorporate ECC?
And if not, why not? And, what's the majority opinion on the
reliability of these memory cards. I'd used this particular
Lexar card many times, so I don't know if the error was a
problem with the card or with the 671. It was running on
batteries, with fairly long mic cable runs, so I suspect
that static electricity may have played a part; no grounding
to bleed static. It was a very cold, dry day.

There are actually two types of flash:

1. NOR flash, which is made in very small capacities, and has individually
addressable cells. The cells are considered reliable, and there is no ECC.

2. NAND flash, used by all flash drives, cards, etc. The cells are
unreliable; it's part of the manufacturing process that they do not write
reliably, and it's all compensated for by writing the data in ECC,
error-correcting-code. NAND is only block-addressable, which gives the ECC a
nice long word length. The combination is very reliable, on paper.

Yet we all know flash drives fail. SD cards are particularly vulnerable,
because they rely on the external equivalent of a disk controller. But your
machine uses CF cards, which do contain integral controllers. If a CF card
fails, it's entirely the fault of the CF card.

There are two types of NAND flash cells: single layer, and multi-layer. The
multi-layer cells store three bits per cell, but have a short lifetime. If
you have a multilayer CF card, you could have worn it out. This would be
unlikely with a single-layer card.


Before the 671, I used a Sony HD Minidisc for recording, and
it worked well. I think I could hook it to the Line Out or
Optical out on the 671 (I think they're active during
recording) for a backup. I haven't tried that yet, but I
sure will!


Thanks,

Jason

It's always good to have a backup.

Bob Morein
(310) 237-6511


.

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