[geeks] Odd NAS behavior with file restores...

[Nathan Raymond]

I've discovered a really peculiar behavior that I'm trying to get to the
bottom of... I had to recently get a new NAS because my old Synology
DS1515+ likely succumbed to the Intel C2000 bug. The new Synology has more
bays, so it's a good opportunity to go from Synology Hybrid RAID (which
works like a Drobo, allowing the RAID to be upgraded with different sized
disks at any time, i.e. convenient but likely very tricky to recover files
from in the event of a disaster) to a RAID 10 (better performance, easier
to recover files from). I plan to re-use some of the drives for the RAID
10, so to transition to the new RAID, I'll need to wipe the old disks,
build the new RAID, and then restore from backup. I have a local backup on
external storage via Synology's Hyper Backup program. Data on the Synology
NAS is a mix of files for various operating systems (UNIX variants, Linux,
Mac, Windows, etc.) going back about 30 years.

Test restoration caused an unexpected discrepancy - when my Synology shares
are mounted via SMB or AFP in macOS, all restored files have an extra 659
bytes added to their size (there were 157 files in my test folder and total
increase in size was 103,463 bytes). Spot checking individual files and
doing a diff showed zero differences in the actual files. Mounting the same
share via SMB in Windows showed no difference in any files sizes (the extra
659 bytes did not appear on any files). My guess is there must be some sort
of metadata that has been added to the files during/after the restore
process, that metadata is Mac specific, and that metadata only gets
associated/seen with the files when they are mounted via AFP or SMB on a
Mac. Copying a file via the macOS Finder from the NAS share to a local Mac
volume retains the extra 659 bytes. Does anyone have any ideas what those
659 bytes of metadata might be? I know that Synology uses the Netatalk open
source implementation of the AFP protocol. Not sure offhand what they use
for SMB.

- Nate