dump(8) verification?

[George Williams]

> >   has anyone hacked dump to perform a verify pass on the data dumped?
>
>     There are several levels of "verify" that one might want:
>
> [1] Read the tape end-to-end just to see if read() returns any errors.
>
> [2] Record the checksum of each block written, read the tape, compute
>     the checksums of the blocks read, and compare.
>
> [3] After each tape, repeat pass IV with the tape write() replaced
>     with a read(), and compare with the disk data.

Under VMS the magtape driver has a write with verify operation that its
backup uses, this could easily be implemented in user code by doing a
write, backing up, doing a read, and then comparing the written buffer
with the read one. Simple, no need to worry about changing filesystems.

Unfortunately slow too. It will at least double the tape IO time (and
make a streaming tape drive stop streaming).

I think this might fit in as 2.5 above.