Newsgroups: comp.unix.xenix.misc Path: utzoo!utgpu!news-server.csri.toronto.edu!torsqnt!geac!gjetor!adeboer From: adeboer@gjetor.geac.COM (Anthony DeBoer) Subject: Re: Need assistance with afio problem. Message-ID: <1991May28.172728.26275@gjetor.geac.COM> Keywords: afio Organization: Geac Canada Ltd. References: <1991May26.203103.19212@chinacat.unicom.com> <29927@hydra.gatech.EDU> <450@yonder.UUCP> Date: Tue, 28 May 91 17:27:28 GMT In article <450@yonder.UUCP> michael@yonder.UUCP (Michael E. Haws) writes: >In article <29927@hydra.gatech.EDU>, ken@dali.cc.gatech.edu (Ken Seefried iii) writes: >> In article <447@yonder.UUCP> michael@yonder.UUCP (Michael E. Haws) writes: >> > >> >It is my impression that you are suggesting that I never keep compressed >> >data on my hard disk, since this data would be subject to the same >> >potential problem when trying to recover it from a tape archive. Or have >> >I missed something? > >Agreed, but the point I was trying to make was that when the compressed file >from the hard disk is now backed up to tape the chances of recovering >it are no better(or worse) than the file compressed during the >backup process. > >Since I was told that it was not safe to compress files during backup, I >assumed that already compressed files would be just as susceptible to >non-recoverability(is that a word?) from a tape archive. The difference is in what you mean by "compress during backup". The easy way to do it is "find | cpio | compress | dd", to compress the whole backup in one pass. An error in the middle of the tape could screw up the decompression for the whole remainder of the tape. Compressing each file individually, though, would make the tape look at if you went through your hard disk beforehand and compressed everything. (That's probably the "easiest" way of trying to implement this; doing it properly is nontrivial.) An error might screw up the remainder of the file in which it lies, but provided you can read the data off the rest of the tape cpio could be re-syncronized on the next header and be able to recover the rest of the files on the tape. There's nothing inherent about compressed files that makes them less restorable from tape than any other file, except for the factor of not being able to decompress past a glitch. Other files, like executables, may also be useless if they're corrupt. On the other hand, of course, a compressed file IS a much smaller target for a glitch to try to hit. :-) -- Anthony DeBoer NAUI#Z8800 | adeboer@gjetor.geac.com | Programmer (n): One who Geac Canada Ltd. | uunet!geac!gjetor!adeboer | makes the lies the Toronto, Ontario | #include | salesman told come true.