on Wed, Jun 29, 2005 at 09:32:41AM -0700, Micah J. Cowan ([EMAIL PROTECTED]) wrote: > On Wed, Jun 29, 2005 at 08:35:21AM -0700, Jonathan Stickel wrote: > > Karsten M. Self wrote: > > > > > > Tape. > > > > > > > I've never really used tape drives, but my one experience was not good. > > Someone else backed up data to a tape on a mid 90s unix machine, I > > think. I needed the data about a year ago. We were unable to access > > the data because we were clueless about how the tape was formatted, what > > software utility wrote to the tape, etc. The computer that wrote to the > > tape was long gone. > > > > From this experience, it seemed that there is no standard when it comes > > to tape formatting, reading, and writing. Has this changed? If not, > > they don't seem that useful to me. > > I have no experience with tape either, but I thought that's what tar & > ar were for? AFAIK, no actual filesystem would be practical, so probably > a tape's content consists of nothing more than a tar file.
Right. Tape is a character (not block) device. a/k/a sequential media. You can't get to some point n+1 on the tape without advancing through n first. This is opposed to disk, where the time to reach any given point is relatively fixed. At worst it's seek + spin: the time for the head to seek to the right cylinder, and the time for the disk to spin to the right sector. For most current [S]ATA or SCSI drives, this is on the order of microseconds. For tape, it's a linear relationship to tape position. There are some tricks to speeding this up, including file markers and the like, allowing you to scan quickly to a given file in a tape. Backup systems can include a directory either on the tape or on disk indicating where a given item is to be found. But you've still got to roll through the tape to get there. Peace. -- Karsten M. Self <[email protected]> http://kmself.home.netcom.com/ What Part of "Gestalt" don't you understand? The pitcher will go to the well once too often.
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