putting a 2 node SL1 HA database env in maintenance

The way InnoDB works this may leave things in a weird state as putting the cluster in maintenance mode does not stop services it just stops the control of the services which allows you to bring down services if you need to or stop a fail over while performing certain actions on the OS layer. 

While snapshots I believe or not supported If you really need to get that snapshot say before you do something major . I would suggest the following as extra precaution to help ensure you have a clean snapshot with MariaDB while using InnoDB Engine.

1. Put Cluster in maintenance mode
2. Stop PaceMaker on the Secondary Node
3. Shutdwon the Primary Node
4. Take Snapshot while powered off on the primary node
5. Power Back on Primary Node
6. set DRBD back to Primary on the Primary Node
7. Disable Maintenance Mode
8. Let services come back on old Primary Node
9. Start PaceMaker back on the Secondary Node

This should keep the state of the cluster before you made the snapshot and if you really need to revert you know that MariaDB was 100% in a non writable mode since the VM was off this way you don't have to deal with redo logs and recovery mode as this can take forever depending on the size of the database but at that point it may be easier to get a temporary clone of the VM as well if your look for a last fall back option if all things go wrong. 

You will also take a IO hit on your drive for the snapshot when you goto remove it if the VM is online and if you are IO bound already when fully running you may get errors and potential slower then normal write performance. 

I would still suggest a Full Backup if you can afford the wait time as well as a restore is always a option if it needs to be done. 

Disclaimer : You should always test your restore plan in a controlled lab environment first if you can

Savage