vcopy -- safe copy

Copy files / directory trees while using write locks, content verify, and the option to use / check / publish content checksum, ...

Goal

Safely copy files across various (local) hardware under circumstances where there may be another file writer active at the same time and/or the (USB?) connection is sometimes flakey or system I/O drivers buggered¹.

Extras: SAFE² operation

As we will use this one for our Qiqqa(R) Sync process among other things, "mirroring" local document libraries to arbitrary local-portable/remote storage, this tool has the additional feature of encryption: files can be encrypted while being copied, thus making vcopy the endpoint for a SAFE² end-to-end sharing/backup system:

SAFE² =

1. SAFE₀ data transfer: the file copies are verified to ensure their content remains undamaged / not corrupted.
2. SAFE₁ from prying eyes: when encryption/decrypion is chosen, the files will be encrypted/decrypted on the fly while copying them to/from the 'unsafe' destination.

vcopy also has built-in counter-measures to ensure that incoming files, which turn out to be corrupted (i.e. not match their published checksums), DO NOT overwrite your local copy: we deem it better to keep your -- possily older -- existing data file than have it blown out of the water by incoming corruption. After all, the sync/fetch can be re-tried later, when the remote side's issue has been fixed; meanwhile, your own data is not gone.

Usage

Command line tool.

See also

For networked / remote storage access, please check out these tools:

• rsync / unison
• rclone (for DropBox, Google Drive, et al)
• zsync (alternative; for DropBox, Google Drive, OneDrive, MegaNZ, ...)

Technology info

vcopy targets scenarios where both source and destination of the copy action are "addressable" by regular file I/O operations, i.e. both sides are mounted disks, which are both accessable by standard tools such as cp (UNIX) and robocopy (MS Windows). When you want to cross network / SSH boundaries which do not match this condition, then we assume you'll be using unison, rsync or similar tools in the next part of your copy/mirror/backup pipeline, while we assume you intend to keep a local 'cache' of the exact same data as is kept at that far-away remote site: vcopy can make sure your local 'cache' is A-okay.

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Footnotes

1. happened to me. Lost several TB of stock material while a possibly buggered Windows 10 rig joined forces with crummy GigaByte hardware to permanently nuke large tracts of data on my external drives. That hurt. To top it off, I discovered while using teracopy (with verify enabled) during the recovery from that (yet incopmpletely diagnosed 😢 ) disaster, that sometimes, if only rarely, copied data would verify as corrupted at the destination drive. teracopy helped recover from that situation, but we need something more universal, OS-wise, for our Qiqqa(R) 'sync path'... ↩