Real world 2nd copy

A normal situation in the enterprise world is to keep more than one copy of a backup.
Usually mechanisms such as robocopy, xcopy, cp are used to transfer files.
This implies that the copy transfers all the archive.
Furthermore, almost always, it is not possible to resume, for example because Control-C was pressed or the connection dropped for some reason.

Something like that

robocopy c:\local \\nas\remote /mir

zpaqfranz does support two kind of "smarter" copy, using the mighty -append switch:

• cp
• r

cp

Suppose we have a 8.3GB .zpaq

 Directory di j:\

20/07/2023  16:03     8.369.547.057 droppa.zpaq

We copy this file to a new folder, with -append

C:\zpaqfranz>zpaqfranz cp j:\droppa.zpaq -to z:\lacopia -append
zpaqfranz v58.10a-JIT-GUI-L,HW BLAKE3,SHA1/2,SFX64 v55.1,(2023-08-25)
franz:-append -hw
Your friendly neighborhood cp/copy
         Space needed             Space frees (        8.369.547.057)
        8.369.547.057         77.983.092.736  j:/droppa.zpaq
Buffer size 1.048.576

--------------------------------------------------------------------------------------
        8.369.547.057   bytes output file
        8.369.547.057   bytes input  file
                    1   files OK
                    1   files expected

3.515 seconds (000:00:03) (all OK)

We write 8.3GB (not a big surprise)

Now update the .zpaq

zpaqfranz a j:\droppa.zpaq c:\dropbox\Dropbox
zpaqfranz v58.10a-JIT-GUI-L,HW BLAKE3,SHA1/2,SFX64 v55.1,(2023-08-25)
franz:-hw
j:/droppa.zpaq:
2 versions, 31.083 files, 8.369.547.057 bytes (7.79 GB)
Updating j:/droppa.zpaq at offset 8.369.547.057 + 0
(...)

8.369.547.057 + (27.960.544 -> 9.597.481 -> 7.589.784) = 8.377.136.841 @ 26.25 MB/s

1.016 seconds (000:00:01) (all OK)

The file is now ~7.5MB bigger Using something like robocopy or whatever takes another ~8.3GB of transfer but...

C:\zpaqfranz>zpaqfranz cp j:\droppa.zpaq -to z:\lacopia -append
zpaqfranz v58.10a-JIT-GUI-L,HW BLAKE3,SHA1/2,SFX64 v55.1,(2023-08-25)
franz:-append -hw
Your friendly neighborhood cp/copy
         Space needed             Space frees (        8.377.136.841)
        8.377.136.841         69.613.543.424  j:/droppa.zpaq
Ready to append 7.589.784 bytes to 8.369.547.057 => 8.377.136.841
--------------------------------------------------------------------------------------
        8.377.136.841   bytes output file
        8.377.136.841   bytes input  file
                    1   files OK
                    1   files expected

0.047 seconds (00:00:00) (all OK)

Only the difference (7.5MB) is transferred