[Info-vax] Backup TK50 tapes

[glen herrmannsfeldt]

Johnny Billquist <bqt at softjar.se> wrote:

(snip, I wrote)
>> The unix read() and write() system calls don't throw away the length
>> information, but the disk file systems do.

>> Now, if you use ibs= and obs= then dd will reblock the data, even if
>> you didn't want it to, but also if you did.

>> But if you use bs= for tape to tape, dd does read for each block,
>> and then write() for the block.
 
> Yes. But what does dd use for the write? The actual size returned by the 
> read, or the size in the bs argument?

If you use bs=, the actual length from the read.

If you use ibs= and obs=, then it reblocks to obs. That is, bs= is
not the same as setting the same value for ibs and obs.
 
> Anyway, this discussion is pretty pointless. dd is just not the right 
> tool, even if you can force it into service under some specific 
> circumstances.

If you happen to be stuck with such, then you might have to use it,
but yes there are other ways to do it.

By now, virtual tapes tend to be much more useful.

-- glen