Duplicacy speed acknowledgment

backup
backblaze-b2

#1

This post is both an acknowledgment of the speed of Duplicacy and a curiosity.

I just performed a 65 Gb backup to B2. Running the backup command again shortly after the backup finishes, it checks that there is nothing new to be backed up in just 5 seconds

INFO BACKUP_STATS Files: 8517 total, 66,085M bytes; 0 new, 0 bytes
INFO BACKUP_STATS File chunks: 61450 total, 66,085M bytes; 0 new, 0 bytes, 0 bytes uploaded
INFO BACKUP_STATS Metadata chunks: 8 total, 6,778K bytes; 0 new, 0 bytes, 0 bytes uploaded
INFO BACKUP_STATS All chunks: 61458 total, 66,091M bytes; 0 new, 0 bytes, 0 bytes uploaded
INFO BACKUP_STATS Total running time: 00:00:05

And the curiosity: How can Duplicacy scan 65 Gb of 8517 local files, compare with the chunks, and find that there’s nothing new in just 5 seconds? :astonished:


#2

By default Duplicacy doesn’t scan all the files if there is a previous backup. Instead, it will just compare the local copy with the latest backup by size and timestamp only. This is what rsync does by default and works quite reliably in practice – it is very rare that a program would modify a file and then intentionally change the modified time back to the original one.

Of course if you’re super cautious then the -hash option is what you want, which can be much slower since all files will need to be scanned.


#3

How many folders are we talking about?

Also, have you tried to run a backup after a system reboot? I’d imagine running a backup moments after a backup completes would be very fast since the OS is caching much of the files’ metadata in RAM.


#4

Yes, I figured it should be doing that, but even that, for +8000 files, and downloading information from the backup in the cloud, it’s very fast … :sunglasses:

I don’t think it is necessary in most cases, and would kill the speed “feature”.

8,517 files in 577 folders:

files

One day later:

INFO BACKUP_STATS Files: 8517 total, 66,085M bytes; 0 new, 0 bytes
INFO BACKUP_STATS File chunks: 61450 total, 66,085M bytes; 0 new, 0 bytes, 0 bytes uploaded
INFO BACKUP_STATS Metadata chunks: 8 total, 6,778K bytes; 0 new, 0 bytes, 0 bytes uploaded
INFO BACKUP_STATS All chunks: 61458 total, 66,091M bytes; 0 new, 0 bytes, 0 bytes uploaded
INFO BACKUP_STATS Total running time: 00:00:06

It’s definitely fast… :yum: