long-morrow@YALE.ARPA.UUCP (03/12/87)
> I do not advise using 'tar | rsh dd' for backing up files on the Apollos. I > was warned that characters can be lost. Sure enough when I went back and > tried to read some of my backup tapes, tar was very unhappy with me. The > occurance of these errors is a function of the load on the TCP/IP network > when the backup is being done. The problem is that a block of data written to a network socket does not necessarily come out in the same size block. This causes the tape to have a random assortment of block sizes, which tar is not fond of. When making a tape, you can fix this with: tar cfb - 20 foo | rsh dd obs=20b of=/dev/tapewhatever the "obs=20b" says to reblock the output into 20*512 byte blocks. When trying to read a backup tape that was written without doing this right, you can probably read it with dd and reblock it, then pipe it to tar, e.g.: dd obs=20b if=/dev/tapewhatever | tar tvfbB - 20 I don't know if apollo's pipes also wipe out block sizes (like 4.2 pipes). If so, their tar should have the "reblock" option (B) that 4.2BSD tar does, which causes tar to keep reading until it has filled a whole block. If apollo tar doesn't take the 'B' option, just leave it off. John Gilmore