Friday, July 22, 2016

Life with Satan's Own Backup: Synology Time Machine Backup goes bad

A few days after my carefully delayed update from Yosemite to El Capitan, Emily’s MacBook Air complained it couldn’t run its Time Machine backups to our Synology DS215j NAS. I can’t say if this was related to El Capitan or not, but I do wonder about El Cap’s relative deprecation of AFP (which Synology/Time Capsule needs).

The usual approach to this problem is to use the Synology web interface to run “File Station” and delete the .sparsebundle from there (don’t even think of trying to do this through the Mac Finder) then start over.

Instead I ran through a checkup of the NAS. I didn’t find anything — but did update my notes on the confusing configuration (every machine has a dedicated Synology username and quota). I tried various things to mount the old sparse bundle including disabling SMB, etc. Nothing worked, I couldn’t make use of the existing backup.

So then I installed a (long!) physical ethernet cable and tried Finder (AF) copying the .sparsebundle to a local drive so I could browse it efficiently. Every time I tried it quit at about 54GB with a message like “The operation can’t be completed because you don’t have permission to access some of the items.” A different 60GB file copied normally.

I figured that was a bogus error message from a corrupt file, so I used Synology to copy the 200GB directory internally. It copied well, no sign of a file system problem. I deleted the original and I was able to Finder copy the Synology copy to my local machine. BackupLoupe could even browse it, because, you know. you can’t use Time Machine to access a backup unless you’re on the original machine (which is why it’s Satan’s own backup).

All very occult.  It’s probably something to do with extended attributes, AFP, and some kind of El Capitan bug.

Oh. And I started over. Of course.

Update 8/29/2020: Backup also failed when I upgraded the old Air from Sierra to High Sierra. Good thing I have alternatives to this TM backup.

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