I soon will have a folder with thousands of files, each file on the order of a few KB. I will need to transfer these across a Windows network from one UNC share to another. In general, is it faster to simply copy the files over en masse, or would it be faster to zip them up (e.g., using 7zip in fastest mode) and send one or a few large files? Or is there no difference in practice?
It is faster to transfer a single large file instead of lots of little files because of the overhead of negotiating the transfer. The negotiation is done for each file, so transferring a single file it needs to be done once, transferring n files means it needs to be done n times.
You will save yourself a lot of time if you zip first before the transfer.
Jon Cahill is very correct, a single file will be faster. However it's worth keeping in mind that if there is any instability in the connection, individual files (or medium-sized groups in zip files) may be better, because if the transfer fails you'll have to start all over again, whereas with multiple files you will just have to re-do the last file started
Lots of little files will also be more expensive to write to the file system than a single large file. It needs to do things like:
- Check the file name is unique
- Write out the file table entry
As you get more and more files in a directory this can become quite costly. And each of these steps can add latency to the copy process and slow the whole thing down.
The average packet size relative to average file size is probably critical here. With lots of small files you may find yourself sending out many tiny packets. Tiny packets still incur TCP overhead; you could wind up doubling the amount of traffic as a result.
Modern systems and even relatively ancient ones can send multiple files over a single TCP connection, avoiding the costs of that handshake.
It's also worth remembering that the choice of protocol affects the overall time to complete - for example, to FTP files from one host to another, can be noticeably faster than using windows file sharing (of course, things like domain permissions and the like are also lost, but in some situations, this can be an acceptable trade off -- After all, these would also be lost by zipping/unzipping)