Tcopy uses 32 bit unsigned to accumulate a count of bytes read/written.

That doesn't work well for tapes over 4G.

I use tcopy a lot to write images of a tape to tape as tape to tape
copying is terribly slow. Slower than it should be. Quickly found out
tcopy can not rewind a file when doing copy/verify.

PR:		11386
Submitted by:	David Kelly dkelly@hiwaay.net
Reviewed by:	phk

1 files changed, 16 insertions, 0 deletions

diff --git a/usr.bin/tcopy/tcopy.1 b/usr.bin/tcopy/tcopy.1
index 32cf748..d201073 100644
--- a/usr.bin/tcopy/tcopy.1
+++ b/usr.bin/tcopy/tcopy.1
@@ -87,3 +87,19 @@ The
 .Nm
 command appeared in
 .Bx 4.3 .
+.Sh BUGS
+Writting an image of a tape to a file does not preserve much more than
+the raw data. Block size(s) and tape EOF marks are lost which would
+otherwise be preserved in a tape-to-tape copy.
+
+EOD is determined by two sequential EOF marks with no data between.
+There are old systems which typically wrote three EOF's between tape
+files.
+.Xr tcopy 1
+will erroneously stop copying early in this case.
+
+When using the copy/verify option \-c
+.Xr tcopy 1
+does not rewind the tapes prior to start. A rewind is performed
+after writing prior to the verification stage. If one doesn't start
+at BOT then the comparison may not be of the intended data.