fail-safe file copy

Posts: 2 · bobby76 17 Mar 2020, 01:22

If I have this off during a power outage, then the files in the original location will be fine, right?

It's only the files in the destination that may get corrupt, right?

Posts: 306 · bgstack15 17 Mar 2020, 19:28

That's generally the case, yes. Reading a file in a modern computer system would not let it be in an indeterminate state that would be easily corruptible the way a file being written to would. That being said, nowadays most filesystems use a process called journaling, which means that they tend to write changes to an up-front area of disk and let the disk write changes later, which makes write operations way less likely to become corrupted due to random outages.

Posts: 7051 · Zenju 17 Mar 2020, 20:17

journaling, which means that they tend to write changes to an up-front area of disk and let the disk write changes later, which makes write operations way less likely to become corrupted due to random outages. bgstack15, 17 Mar 2020, 19:28

Just to clarify: "pulling the plug" (either power outtage or cuting the network connection) has an about 100% "success" rate of corrupting the target file that is currently being written to, including all other files that have yet un-flushed changes somewhere in the caches (either OS or hard disk). Therefore fail-safe file copy is an absolute must-have option (at least if you consider your data important...)

Posts: 2 · bobby76 21 Mar 2020, 20:03

Thank you, bgstack, for the answer. I was more concerned about the original files over the copies.

And thank you, Zenju, for the wonderful program.

Posts: 16 · Webguy1 8 Sep 2022, 19:43

If I have fail-safe file copy off, the worst thing that will happen is a file will not get synced to my backup, right? And I assume that will be in the log? Then next time it runs, it will sync it?

Posts: 7051 · Zenju 9 Sep 2022, 07:10

If I have fail-safe file copy off, the worst thing that will happen is a file will not get synced to my backup, right? And I assume that will be in the log? Then next time it runs, it will sync it? Webguy1, 08 Sep 2022, 19:43

No. The worst case is silent data corruption without any indication, and no logs.

Posts: 16 · Webguy1 9 Sep 2022, 17:28

Ah, good to know. Does this happen enough to be worrisome for the average "not essential" nightly "just in case backup" sync? Like the next night it will be corrected?