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From: "David E. Fox" <dfox@tsoft.com> Date: Sat, 13 Jan 2001 11:08:37 -0800 To: "Mike O'Neill" <mikeo@redhillstudios.com> Subject: Re: [svlug] using a tapedrive Cc: svlug@svlug.org On Friday 12 January 2001 14:23, you wrote: > Okay newbie question here. I just attached for the first time a tape > drive. Anyone know of a good online howto for using tar and the drive? Man > tar is nothing more than a command reference. Using tar with tapes is just about like using tar with any other device. The one big thing to remember is the difference between your normal tape device (which rewinds) vs. the non-rewinding tape device. The first tape device is usually going to be /dev/st0, and the non-rewinding tape device, which is usually /dev/nst0. If you're going to use 'mt' to position the tape (think of this like index marks on a VCR) you want to use the non-rewinding device, otherwise the tape will seek to the desired spot and rewind. This can be disastrous for your backup if you do something like: # tar cvf /dev/st0 /home #backup /home # mt -f /dev/st0 fsf 1 # move to the end of the first archive # tar cvs /dev/st0 /var #backup var, which just wrote over the /home backup Clearly, you wanted to use the non-rewinding device there. Basically, you can write to the tape with tar just like another device: # tar cvf /dev/st0 / # this will back up everything Some flags are useful, although optional. If you want to restore a functional system, you should use -p (--preserve-permissions) which extracts the original permission bits and ownership info from the other archive. Otherwise, it just uses the default umask values when creating 'new' files on your filesystem. I tend to use --block-size to give tar bigger blocks when writing to tape. > How can a tell how much space is left on a tape? I don't think you can. But you can guess how much space a backup will take by using 'du'. But this is likely going to vary because of block sizes and inter record gaps and such. > How do I extract an archive to a specific path other than the current dir? tar normally doesn't include a leading '/' so what it writes is relative to wherever you happen to be. This is important to know when you do a restore, to be in the same place in the filesystem you were when you did the backup :). ===