RAID Parity Applications For Cheap Media? 13
yamgirl asks: "I've been reading up on RAID strategies for protecting against hard disk failure, particularly those RAID levels that involve recording parity on one disk to duplicate data on multiple other drives, and I've been thinking that this would also be wonderfully useful in making backups to CDROM, or even floppies. Many's the time when I've had a bagful of floppies with me, trying to install something, and found that one floppy out of the batch had crapped out, rendering the rest useless until I went home and got a new copy. If I could make a RAID-style parity disk whenever I needed to make multiple-volume disk sets, I'd only have to carry around three extra disks (one blank to write a new copy on to in case of emergency, and one disk to keep the recovery software on - but the latter two I'd just need one each of for any number of separate sets of parity disks and multi-volume sets of media.) as very effective insurance against crappy disks. Much cheaper in time and effort and disks than making entire extra copies of multi-volume sets, or for that matter of needing to go off site to track down a new copy. ANYHOW, my question is, has anyone ever seen or written any software to do this, to generate parity disks and to recover lost data with them? (And is it free? =)"
3ware ATA Raid Controller? (Score:1)
It's been done with CDs (Score:1)
Re:It's been done with CDs (Score:1)
why ? (Score:1)
read a bit more about RAID - its slightly different to what youre thinking.
Re:why ? (Score:1)
Maybe possible on linux, but floppy isnt feasible. (Score:1)
I think it's better to make the image file(s) of the floppy disk(s) and backup the entire sets and imaging program to more reliable and useful media like CD-R(though it's not that reliable, too) or your notebook(it's cumbersome though) before going out so that you'd only have to carry one additional CD (or heavy notebook) and one additional blank floppy to reduce the chance of disaster. Anyway, if you have large piles of the floppy backups already, you should backup these unstable magnetic timebombs(with random timer setup) to other media as soon as possible!
It would make more sense to use a new disk format. (Score:1)
This isn't rocket science, and it wouldn't be all that difficult to do the same thing today. All you'd really need to do is to create a disk format that allows you to scatter file data across the floppy and reserve some fraction of the disk for parity or Hamming code sectors, which you use to reconstruct any sectors you lose. You'd have to be sophisticated about where you arrange your data (if you lose too much of the redundancy for any one part, your data is still toast) but this would allow you to manage things on a single floppy. Now that I think about it, it shouldn't be too hard to make a parity file which occupies certain tracks (say, the inner 8 tracks) and use the sectors on those tracks as parity for the other 72. With a little sophisticated software, you could recover any single lost sector or track.
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Re:why ? (Score:1)
Err... floppies? (Score:2)
The only thing floppies should be used for nowadays is propping up wobbly tables.
- A.P.
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"One World, one Web, one Program" - Microsoft promotional ad
Re:It would make more sense to use a new disk form (Score:2)
Simple parity? (Score:2)
If you have nfiles each one-floppy big (arj1 to arjn) you can then generate a final parity file by simply xoring all the nfiles together, to give a file equal in size to the largest file that makes it up. should any single floppy in the set fail, then exactly the same utility will allow you to xor all the remaining files, plus the parity file, and gain back the original (missing) file.
obviously this will only protect you from ONE missing disk however, but it is better than nothing
I imagine you could do the same thing on a disk-image basis, but it would require much more specialized access to the low level floppy calls to get "raw" reads of the disk sectors for the operation, whereas a simple file XOR can be knocked together in MS Quickbasic in five minutes, and as a under-one-k executable in ten :+) - if you don't want the bother of writing one yourself, a simple websearch on One Time Pad implimentations will turn up several dozen - with source.....
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Not that hard.. (Score:2)
I wouldn't do it with floppies. Disk images on a bootable CD-R/RW work quite well. If a disk craps out, boot to the CD and make a new disk image. Writing a bootable CD with a small Linux or *BSD install and all of the images is easy. Of course, that means you have to carry (n + 1) + backup CD, but that shouldn't be terrible.
Re:It would make more sense to use a new disk form (Score:2)
You'd need at least nine disks in the set, and you'd have to carry (n>9)+1 disks (the extra disk being the rebuild utility) but they would seem to any unknowing PC to be ordinary install media. No custom filesystem, and probably easy to implement.