How does Truenas track snapshot age/deletion?

[ddrucker]

In Periodic Snapshot Tasks, you set a Snapshot Lifetime. Where is that lifetime actually stored?

Suppose I have weekly snapshots kept for 3 months and also hourly snapshots kept for a week. Both share the naming schema auto-%Y-%m-%d_%H-%M.

How does the system know which snapshots to remove when? It clearly knows and does it correctly; I'm just wondering about the mechanism.

 

[sretalla]

There was a thread around somewhere where it's discussed.

Going from memory, there are 2 answers:

1. For replication tasks, the management of snapshots according to the replication task settings is done by zettarepl (the tool used to actually do the replication).

2. For periodic snapshot tasks, the task itself (possibly together with the middleware) is doing the job... as far as we can tell.

 

[sretalla]

Considering that snapshots have a property that keeps track of their creation date. I'd imagine it's just a simple date arithmetic from the creation date to the current date.

I think it's more complex than that as there are naming triggers... in fact I think in the other thread we came to the conclusion that it's not using the creation date (at least not in all cases).

 

[Whattteva]

I think it's more complex than that as there are naming triggers... in fact I think in the other thread we came to the conclusion that it's not using the creation date (at least not in all cases).

Ah that's interesting. Does the database come into play also?

 

[sretalla]

This is the thread I'm talking about (I think)

How are Periodic Snapshots marked for deletion?

I could never find a definitive answer to this particular question. What exactly runs behind the scenes to mark and delete old snapshots? Is there a script that searches for old snapshots based on their name? Or is it based on their creation timestamp? Is it more sophisticated where it stores...

www.truenas.com

The last post by @winnielinnie covers it pretty well.