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User profile for user: Orj
Orj Author
User level: Level 1
66 points

Photos.app xattr: how vital are they??? (strange behaviour of rsync -X on ExFat drive)

Can somebody explain how extended attributes are used by Photos.app? This appears to be a plausible origin of the nightmare I'm in since 3 months with my libraries.


Maybe you don't know it, but the files in a .photoslibrary bundle have extended attributes. These can be seen with $ ls -l@, eg:

MacBookJO/V/B/P/M/2/1/1/20181210-061108> ls -l@ IMG_3212.JPG 

-rw-r--r--@ 1 orloff  staff  3144231 18 nov 09:49 IMG_3212.JPG

com.apple.cscachefs     70 

com.apple.quarantine     21 


Now, these attributes are usually handled on non-HFS+ external devices by storing the extended attributes in a 'hidden' file named ._IMG_3212.JPG next to IMG_3212.JPG .


This is what is happening when making a remote backup of the library (with rsync -X) on an ExFat disk connected to my Wifi server: any file.jpg or directory comes together with ._file.jpg or ._directory files.


However, when I backup on the same disk directly connected by USB to my computer to save backup time, with the same "rsync -X" command, the first thing it does is to delete all ._* files. This is because it can apparently save the extended attributes in the ExFat filesystem when connected by USB.


Maybe this is a bug in rsync? My version is 3.1.3...


But I come back to my original question: how is this information, eg quanrantine, used by Photos? What happens if it is wrong, and how to fix it?


Posted on Dec 16, 2018 5:02 AM

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User profile for user: léonie
léonie
User level: Level 10
197,751 points

Dec 16, 2018 5:23 AM in response to Orj

I cannot help with the main question you posted, but you have a more serious problem with your backup scheme than the attributes.

The file system format(EX-FAT) of the drive is unsupported, and you are accessing the library over a network. Both issues can corrupt the library because of wrong pathnames, permission errors, or race conditions when accessing and updating the library.

And the "Ignore Ownership" flag is required as well,, to prevent permission issues.


Remember, that Apple only guarantees the correct operation of Photos within these specifications:


See this link: Move your Photos library to save space on your Mac - Apple Support


You can store your library on an external storage device, such as a USB or Thunderbolt drive formatted as APFS or Mac OS Extended (Journaled).1 Find out how to check the format of your external storage device. 
To prevent data loss, Apple doesn't recommend storing photo libraries on external storage devices like SD cards and USB flash drives, or drives that are shared on a network.

I would really switch to a backup that is guaranteed to work and does not rely on smart workarounds, or you may find yourself without a working backup, when you need it most.


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Photos.app xattr: how vital are they??? (strange behaviour of rsync -X on ExFat drive)

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