Timeline for Does Lightroom actually rewrite the *ENTIRE* DNG file on every metadata change?
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| Apr 13, 2017 at 12:43 | history | edited | CommunityBot |
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| Sep 4, 2016 at 9:34 | comment | added | LaVache | @MichaelClark My question is really about what Lightroom does, not the OS/filesystem. All common OSes & filesystems support editing files without rewriting the entire file. A 1 byte change to a 100GB Truecrypt volume or VM image file doesn't ever cause 100GB to be rewritten to disk, that would be useless. Where did your information come from regarding Lightroom rewriting the entire DNG file to disk instead of just modifying it? (for metadata changes) | |
| Sep 4, 2016 at 4:22 | comment | added | Warren Young | Re: My comment above about the "entire file" being rewritten, I've just repeated my tests, and this time I get different results. I suspect I was just sloppy in my original test, rather than the behavior of Lightroom changing since the last test. The main thrust of my comment above stands, however, which is that the results will be independent of the filesystem. CoW doesn't silently change application behavior to turn whole-file rewrites into partial-file rewrites. It only affects the safety of doing so. | |
| Sep 4, 2016 at 4:18 | comment | added | Warren Young | Re: conflicting comments, this is exactly what I meant when I said that I think you're confused. My comment on your other answer is only addressing the data safety issue you brought up; CoW doesn't affect the application's I/O behavior, it only tells you what the filesystem does on disk as a result of the application's I/O. Most any tutorial on ZFS will explain this. Here's a quick summary of ZFS. | |
| Sep 3, 2016 at 18:22 | history | edited | Michael C | CC BY-SA 3.0 |
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| Sep 3, 2016 at 18:13 | history | edited | Michael C | CC BY-SA 3.0 |
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| Sep 3, 2016 at 18:13 | comment | added | Michael C | @WarrenYoung Your comments to this answer seem to be arguing the exact opposite of your comments here: photo.stackexchange.com/a/79564/15871 | |
| Sep 3, 2016 at 18:05 | comment | added | Michael C | I'm not sure the second paragraph implies at all what any particular application does, only that some of the cutting edge file systems allow for the possibility of leveraging such capabilities in the future that may change the current reality which is the primary gist of the answer.. | |
| Sep 3, 2016 at 4:50 | comment | added | Warren Young |
I haven't tried it with APFS yet (I avoid beta OSes), and I don't use Lightroom on Windows Server (the only way to try ReFS) but I can tell you that your statement about ZFS is wrong, and I doubt it's correct for APFS or ReFS. I ran Lightroom CC 2015.mumble on OS X 10.11 with O3X ZFS a few months ago under truss and watched it write out the entire file on every metadata update. I think you're getting confused by the CoW feature of these file systems, which merely avoids a complete file rewrite when the app touches part of the file only; if the app doesn't play ball, the FS can't save you.
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| Sep 2, 2016 at 18:59 | history | answered | Michael C | CC BY-SA 3.0 |