dump(8): how many bytes written to tape?

Oliver Fromme olli at lurza.secnetix.de
Wed Nov 15 03:45:15 PST 2006

Ulrich Spoerlein wrote:
 > I'm trying to figure out how much bytes were written to a tape by
 > dump(8). I'm using a blocksize of 64kB to maximize throughput to the
 > tape drive. Initially, I thought I could just add up the number of
 > "tape blocks" written by dump and multiply by 64kB. But it looks like
 > dump is still reporting those values as 1kB blocks.
 > [...]
 > So, how exactly is the '-b64' parameter to dump(8) affecting the block
 > size on tape?

The -b option does _not_ change the blocksize of dump,
which is hardcoded at 1024 bytes and cannot be changed.
That means that the reported number of blocks is also
always measured in units of 1024 bytes, no matter what
your -b option says.  Unfortunately the manual page is
somewhat misleading.  :-(

Instead, the -b option changes the number of blocks per
record, i.e. how many blocks are written at once per
write operation.  The default is 10 for standard tapes
and 32 for high-density tapes (>= 6250 bpi).

Best regards

Oliver Fromme,  secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing
Dienstleistungen mit Schwerpunkt FreeBSD: http://www.secnetix.de/bsd
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