Date: Sat, 27 Oct 2001 12:33:06 +0200 (CEST) From: Nils Holland <nils@tisys.org> To: freebsd-questions@freebsd.org Subject: Funny things to do with tar... Message-ID: <20011027121324.O692-100000@jodie.ncptiddische.net>
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Hi folks, well, in the following I will talk about some strange experiences I have recently made usig "tar". Probably some of you will have some suggestions as to how to make my future tar-esperiences less strange. In that case, I'd be glad to hear about it! Ok, the situation was like that: I started investigating in the possibility of using tar together with CD-RW media in order to back up my system. I thought the best thing I might do was trying it out under real world conditions, which means creating a backup of machine 1 and then extract it back to machine 2, which I have put together especially for this test. So let's do it, I thought, and had a look at the tar man page. I decided that I could simply use tar with the standards -c option, then tell it that I wanted multiple volumes (-M) and that the volumes should be CD-sizes (-L). I started tar like that, created multiple .tar files on my hard disk, and burned them on CD. Note that I made an ISO-fs of each .tar file first, as pervious experiences have shown that burning a "raw" .tar file to CD causes problems that manifest themselves that during the extraction process tar will not be able to detect the end-of-file, so it will abort with a lot of read errors once it has reached the end of the first CD. Making an ISOFS from each .tar file solves that issue. Let's go ahead: Finally, all my CDs were ready, containing the complete /usr partition of my work machine. I then headed over to my test machine to restore the CDs. It did in fact work, without any obvious error messages! The problematic part begins here: Upon having extracted the tar-CDs, I tried to see if the extracted data was actually usable. In order to find that out, I decided to start a few programs and see if them run. Interestingly, when I started X with KDE, KDE didn't want to start. kdeinit (as well as several other KDE processes) crashed and dumped core. I tried to investigate on that issue, but without luck. Eventually, I erased the whole /usr partition on my test machine, and used NFS to directly copy /usr over from my work machine to my test machine. After that operation had completed, KDE would run again! So, what have I learned? Obviously, the data extracted from my .tar-CDs was at least partly corrupted, as copying the same data via NFS worked. All of this makes the issue extremely complicated: I don't know if the data got corrupted during creation of the .tar files, during the burncd process, or during the extraction process. Furthermore, I don't know if I should probably look for the fault in the CD-RW writer, in the CD-ROM drive that read the data, or if I should suspect I have bad CD-RW media. All I know is that a backup process like this is not a good thing to use for actually backing up important files. So, any suggestions? Is anybody using tar + CD-RW and can tell me about successes or similar failures? Any ideas how I can better make sure that the data on my CD-RW media is actually in good working condition? I'd be glad to hear about anything related to this issue! Greetings Nils Nils Holland Ti Systems - FreeBSD in Tiddische, Germany http://www.tisys.org * nils@tisys.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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