--As of June 29, 2014 7:48:19 AM -0700, jerry is alleged to have said:
The real problem here is that I really shouldn't change the data set while backing it up, right? I really can't afford to have this data sit without write access for multiple days. Totally impossible.
Yes and no... Yes, if you want a consistent point-in-time backup, you can't modify it while it's backing up. No in that you can modify it and it won't mess up tarsnap.
Tarsnap will behave like any other Unix program (on Unix, at least); meaning that once it opens a filehandle the OS will hold that version of the file around until it's done with it. It only ever reads one file at a time, so each file will be backed up in the state it was when tarsnap got to it. It won't know about added files after you start the backup, and it will throw warnings about ones that leave but it doesn't die just because of them.
So if you backup an in-use filesystem and create files in it, they will be ignored for that backup. If you edit files, they may or may not be backed up in the edited state. If you delete files, they may or may not get backed up first. Depending on what you are doing, this may be acceptable. (It's typically not for databases, but usually is for personal files.)
If I copy a snapshot off to another device or tar file, and then tarsnap off of that, will the transfer-only-changes feature still work when I do subsequent tarsnaps of the original data?
I believe so (I think tarsnap doesn't care about the file path, only it's hash), but I won't say for sure.
Daniel T. Staal --------------------------------------------------------------- This email copyright the author. Unless otherwise noted, you are expressly allowed to retransmit, quote, or otherwise use the contents for non-commercial purposes. This copyright will expire 5 years after the author's death, or in 30 years, whichever is longer, unless such a period is in excess of local copyright law. ---------------------------------------------------------------
