APFS and session file backup / auto saves ???

[BusyBoxSt7]

Has anyone found this to be an issue yet or am I not understanding this correctly?

If in APFS common data is only stored once (to save space), then if one session file is corrupted, unless it's in the new/different part of the data, aren't they ALL corrupted? This would mean that your work is only as safe as the last time to backed it up to a different drive. I know for something to be "safe" it has to exist in 2-3 different places, but drives crash much less frequently than files get corrupted. Point being that if this is an issue, one major use of session file backups is rendered basically useless because it has to be copied onto a different drive or cloud to be safe.

Did I misunderstand this?

[Darryl Ramm]

Yes you misunderstand this, that is not how sessions work on APFS. They don't do anything fancy with APFS.

"drive crashes" should not be the top of your concerns for data loss. Got a mirror handy? The top thing you should be worrying about is user error.

[BusyBoxSt7]

Darryl,

Drive crashes are not my concern at all. Perhaps re-read what I wrote, or maybe I've written more clearly below.

APFS shares data between files. Every session file backup is probably 90% the same data, so it's **shared**, meaning if it's corrupted in one session, are we not screwed for all the backups? My point is that if a session gets corrupted, on HFS, this has nothing to do with any other session file backup, so you go find a recent session and start where you left off. In APFS, if that 90% the same data gets a corruption in it, which is not ultra rare in Pro Tools, then not only is the current session you're trying to open corrupt, it's likely the whole d*mn song is lost because APFS only kept 1 copy of that similar data between all the autosaves/session file backups (... song pretty much screwed unless all the takes started from the beginning).

I only mentioned drive crashes as a comparison, because that's what regular backup schemes (I mean to drives or clouds, not Pro Tools' autosave function) are based around -> "what if my drive fails". That's not my concern though, just mentioned to differentiate the 2 kinds of "backups" and why each one exists.

Stephen

[BusyBoxSt7]

Source -
https://eclecticlight.co/2020/04/14/...apfs-a-primer/

"Take for example a 100 GB video file [or whatever file, could be your 3MB backup, right? Or is there a size threshold?], from which two copies are made to enable changes to be made to the end. When those edits are complete, the structure of the three files is:
File 1: ABC
File 2: ABD
File 3: ABE
with A and B as data common to all three, resulting from the original cloning. If corruption now occurs to the data in A or B, all three files become corrupt unless that takes place through the file system and triggers the use of separate storage. Thus, failure in a storage block or ‘bit rot’ damages all three files at once. Currently, there doesn’t appear to be any means of discovering which data are common to more than one file, which makes this difficult to detect or understand. All the user will see is that suddenly all three files are broken. Neither are there any tools capable of ‘de-cloning’ files."

[Darryl Ramm]

You are reading about advanced features of a file system that Pro Tools does not use. None of this is a relevant. You are creating a worry out of nothing.

[BusyBoxSt7]

Originally Posted by Darryl Ramm

You are reading about advanced features of a file system that Pro Tools does not use. None of this is a relevant. You are creating a worry out of nothing.

My bad - apparently this only applies to when you click/duplicate a file anywhere in finder, not to other files... If I'm understanding this correctly. The article does say that finder will use cloning whenever possible, but only in the context of manually making copies of stuff I think, so not the auto-saves.

[Darryl Ramm]

Originally Posted by BusyBoxSt7

My bad - apparently this only applies to when you click/duplicate a file anywhere in finder, not to other files... If I'm understanding this correctly. The article does say that finder will use cloning whenever possible, but only in the context of manually making copies of stuff I think, so not the auto-saves.

Its talking about COW (Copy on Write) files that get made using the new filesystem API extension clonefile(). Pro Tools has not been rewritten to use clonefile() and might never be. So it's all irrelevant.

But even if it was your worry was about disk failure... human error like deleting a dependent child of COW disk never deletes the parent parts if there are other files relying upon them. And disk failure is just very rare... most backups are used to recover from human error. And that get to be a factor in considering how they should be used (esp. not left connected/mounted on the system where us idiots can get at them).

(The first COW disk technology many folks saw were the virtual disk, undoable disk, and snapshots features in VMware products. Something I helped get to market. We did not invent the idea (some of our folks had done academic research on related technology), but it was one of the first time that end-users could see the power of that technology in a usable way).

[BusyBoxSt7]

Roger all that. Good info. I will say though I’ve had a good handful of drives die. SSDs as well. It’s rare but still an issue every few years (and I’m not even a heavy user per se).