If you are going to use any off-site, third party, or really ANY back up strategy in addition to Filemaker Server, just be sure that:
A) you NEVER backup the live database file
B) you ALWAYS close the hosted database before performing the backup
C) you schedule a Filemaker server backup first, then use Datto to make a backup of the backup you just made in the Backups folder.
Again...don't backup from the Database folder under any circumstances. And be sure that you close the live database file during the Datto backup for good measure.
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Most of the modern backup providers like this one leverage the Windows Shadow Copy / Snapshot technology (VSS) StorageCraft may go one step further and use some block-level reading (as opposed to file-level reading) but it is not clear from their websites.
FMS is not VSS-aware and not VSS safe. If you were to take a VSS-based backup and you restore from it you will find that all FM files are reported as 'improperly closed' at a minimum and potentially damaged at worst. That's because requires absolute monopoly on access to those files to make sure all data is safely written to it. No other process should be allowed to touch the files. No Anti-virus, no indexing, no 3rd party backups.
When FMS makes its own backup it sets a flag in the file and very briefly suspends user activity so that its cache can be written to the file. FMS does not get that opportunity when a 3rd party backup grabs a copy of that file. FMS looks for that flag when it tries to open a file. Worst case FMS was actively writing to the file at the moment the 3rd party backup grabs it so the file may get corrupted that way.
If you want to use a backup mechanism that is based on VSS then you have to put FMS in paused mode from the CLI and resume after the backup. Which sounds easier said than done. The tools are there and easy to use but getting the whole sequence and timing right is not always so easy. Which is why the best practice is to just avoid that risk and not use 3rd backup backups on the live files.
Very helpful! Thanks so much for responding to my request.