Do I need backups with multipled synced computers?

My DT3 databases are synced via Dropbox to 4 different computers which I use in various office or travel situations.

I am pondering if and why I need to also do a backup to Time Machine or a NAS or something else similar.

If any one of the computers crashes, it would be simple to restore the data from the Sync store.

If I were to use DT3 to delete something important in the database, I could restore it from the Trash in DT3.

Do I still need a conventional backup in case somehow there is a Dropbox sync bug that propagates file deletion across all of my computers? What scenario might require a conventional backup rather than multiple synced backups?

(For purposes of this question, ignore the beta aspect of DT3 and assume that this is a question for use of the final non-beta version of DT3.)

Regardless of the version or beta status, sync is not a backup, neither advertised nor advocated as such. So yes, you should be observing a proper primary backup strategy using TimeMachine (or similar snapshot-style backup applications) and external drives. Also, you should read the recent series of articles we posted:​

Yes, I recognize that has long been your recommendation.

Can you suggest to me a scenario where Syncing to 4 computers to Dropbox could blow up in my face and cause me to lose significant data? It seems to me I do have backups - each of my computers has a full backup of the data.

Just speaking of syncing:
What would you do if there was some corruption in the sync data and you deleted your database on the Mac?
Not only would you have no recourse from the sync data, but also consider if your network connection was down or Dropbox’s servers weren’t responding quickly or at all. (And don’t think that never happens. It is far more common than you imaging.)
If you had proper local backups, you would be up and running much faster.

It seems to me I do have backups - each of my computers has a full backup of the data.

Are you merely referring to having a copy of the database on each machine as “a backup” ?
If so, that is a natural byproduct of the decentralized data model, but it is not considered a backup. If all the machines are in the same location, it could be used that way, just like sync offers some of the functionality, but that is not the intended purpose.

In fact, the best backup strategies also involve off-site backups, archived in a more secure location. This is often a safe-deposit box or other storage facility, depending on the needs.

As it turns out, I have a somewhat unusual configuration of my main workstation. In order to support six high-resolution monitors (often all running DT3 simultaneously - yes I am addicted and make immense use of the software) I run two Macs with Synergy software operating one mouse/keyboard so they all appear to be part of the same primary computer. Those two “main” computers both Sync to Dropbox.

So yes, I do have two “local” copies of DT3 data for that reason.

I guess my question is - is Dropbox sync corruption something truly that has been known to destroy Devonthink databases or is that just a theoretical (albeit valid) possibility?

Theoretically it’s possible although I can’t remember such an issue for a long time. But what about this scenario - you accidentally delete items on one Mac and this change is synchronzied before you notice it. Wouldn’t backups be really useful then?

Ideal (not only in case of DEVONthink) are always both local and remote backups including older versions (not just a copy of the latest version, this would be useless again if you notice an issue too late).

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What if you just accidentally deleted some data in a Dropbox location? That deletion could (should) get synced to all the other locations. You’d be relying on Dropbox history/versioning. To mitigate that scenario why not have at least one true backup location that wasn’t vulnerable to any of that?

In addition to the ‘sync’ side of things I use regular physical disk cloning and regular Arq offsite backups which backup versions to a different Dropbox location that’s ‘selectively synced’ to be invisible to the Finder and thus not susceptible to inadvertent deletion. You can also use other offsite choices like Amazon S3, Backblaze, etc.

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Yes that would be helpful - particularly with multiple backup versions in case I do not notice the deletion immediately.

But I do have a question there - is it valid/recommended to backup a DT3 database while the application is running? If yes, that’s great - I know many databases do not recommend that because there can be corruption issues with transactions in progress. If no, then does that mean after doing any major data entry or import on DT3 I should shut down the software or at least close the database and back it up manually?

It’s not recommended to backup opened databases.

This does depend on the backup method you’re using. Time Machine does a snapshot-style backup (which I consider the safest method), so it captures the data at one point in time, even if you’re continuing to use the database after and while it’s doing its backup. However, to be extra careful, you can certainly close the databases before initiating any backups.