Re: backup archive format saved to disk

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On 12/05/06 19:33, Douglas Tutty wrote:
On Tue, Dec 05, 2006 at 06:57:38PM -0600, Ron Johnson wrote:
>
You could implement your own FEC. A very simple form of FEC is simply
Yes, but *why*? Tape storage systems have been using ECC for decades.

There's a whole lot of "Linux people" who's knowledge of computer
history seems to have started in 1991, and thus all the many lessons
learned in 30 years of computing are lost.


Hi Ron,

I'm hoping someone who can remember computer history prior to 1991 can
give some perspective.

It think (__please__ correct me if I'm wrong) that the tape systems had
the ECC as part of the hardware. Write a plain datastream to the drive
and the drive did the ECC part transparent to the user. Read the data
and a bad block gets fixed by the hardware ECC.

I'm told that modern hard drives also do ECC but I can't find out how
that is implemented. I'm told that if a block starts to fail (whatever
that means) then the data is transferred to a new unallocated block,
transparent to the rest of the computer. Only if the drive runs out of
unallocated blocks does it give errors.

The question is, if a block is sucessfully written now, if the drive is
not used for 5 years then a read is attempted, is the drive able to
retreive that data using ECC (as a tape drive could)?

Mike is correct, disk drive blocks do have ECC.

Remember, though, that drives are delicate mechanisms, and so the
problem I see is the lubricating oil possibly thickening, and thus
the drive not spinning up properly. Hopefully the bad spin-up would
not cause the r/w head to gouge the platter. Otherwise, the data
could still be retrieved, easily, for a price, from a data recovery
company.

[snip]
In the absence of an all-in-one archive format, I'll use tar (which can
detect errors just not fix them) to take care of names, owners,
permissions, etc. Then that tar needs to be made ECC and compressed.
If I want to throw in a monkey, I'll consider encryption.

Remember what "tar" means: Tape ARchive. It's designed as a
container file.

OTOH, if you're backing up a hard disk, you could do file-by-file
backups, compressing the big, compressible files, and leaving alone
the not-so-compressible files. Thus, if a sector goes blooey,
you've still got most of your data.

Yes tape drives do that. Its probably why they cost so much. Hard

And lower production volumes.

drives are much cheaper and are supposed to be able to hang on to their
data (Seagate gives a 5 year warranty). But having seagate give me a
new drive when I can't get my data off after 4 years is cold comfort.

The other problem with tapes is their fragility. Drop a DLT and I'm
told that its toast. Put that tape in the drive and I'm told it can
damage the drive.

We've used DLT drives for years, and never had that problem.

A laptop drive in a ruggedized enclosure is much more
robust and has a wider environmental range.

Drop a HDD and you've got worse problems.

Perhaps what I'm looking for doesn't exist. If it doesn't, I'll start
work on it.

As far as computer history prior to 1991, I could never get the hang of
C. I'll stick with fortran77.

Give me VAX COBOL. But then, I've always been on the DP side.

- --
Ron Johnson, Jr.
Jefferson LA USA

Is "common sense" really valid?
For example, it is "common sense" to white-power racists that
whites are superior to blacks, and that those with brown skins
are mud people.
However, that "common sense" is obviously wrong.
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