-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 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. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (GNU/Linux) iD8DBQFFdjcNS9HxQb37XmcRAnHsAJ9c5OekXV/Q6K9DPIpWN7OZy4AQHACeKRQE hlA1v/E/xXqysk0iholtU84= =8624 -----END PGP SIGNATURE----- -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
