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- Path: sparky!uunet!sun-barr!ames!agate!violet.berkeley.edu!bartlett
- From: bartlett@violet.berkeley.edu (Paul Bartlett/Gary Shea;Lat 841;;;MV86)
- Newsgroups: comp.sys.sgi
- Subject: help in understanding tape blocks: dd, bstream, tar
- Date: 15 Aug 1992 03:43:20 GMT
- Organization: University of California, Berkeley
- Lines: 58
- Distribution: na
- Message-ID: <16hugoINNr9s@agate.berkeley.edu>
- NNTP-Posting-Host: violet.berkeley.edu
-
- Situation: Machines: Indigo, 4D70/GT Running 4.0.5
- Tape drive (4D70/GT, from SGI): ARCHIVE: VIPER 150 21247-005 VP1
- Tape drive (ditto, from ANDATATO): EXABYTE: EXB-8200 2618
- Tape drive (Indigo, from SUN): ARCHIVE: VIPER 150 21531-004
-
- The following happens on all three combinations.
-
- What I'm trying to do:
- use tar with bstream as per the bstream man page to make backups
- and distribution tapes for customers to use.
-
- so, I do
-
- (1) tar cf - Mail | bstream -o/dev/tape
-
- and then, I do
-
- (2) bstream -i/dev/tape | tar tf -
-
- and get a listing of most of my directory, then a message:
-
- </dev/tape> Change tape and type RETURN or "quit":
-
- and if I hit return, I get the rest of my directory, and the
- message again.
-
- If I try
-
- (3) tar t
-
- directly, I get some of my directory (less than before), then
- a message
-
- Change tape and press the Enter key:
-
- and if I hit return, I get the rest of my directory.
-
- If I do
-
- (4) dd if=/dev/tape | tar tf -
-
- *then* I get the whole directory. This also works if I put a
- bstream into the pipe.
-
- I tried to look at bstream's debugging output with no enlightenment;
- this also happens no matter what combinations of blocksizes and blocking
- I use (the speed, of course, varies dramatically).
-
- Now, I don't know much about tape drives, so I can't tell what's
- happening here. If this is indeed the expected behavior, I'd like to
- understand what is going on, and know if there is a workaround so
- bstream-written tapes can be read by tar without trouble; if this is
- supposed to work, I'll file a bug report. I'd sure like to be able to
- use bstream to write the exabytes for our customers, it really helps
- the speed on a loaded system.
-
- Georges Lauri
- lauri@gall.cchem.berkeley.edu
-