The mail archive seems to indicate this list is appropriate for not only the technical coding issues, but also for user questions, so I wanted to pose a question here. If I'm wrong about that, I apologize in advance. The page https://btrfs.wiki.kernel.org/index.php/Incremental_Backup talks about the basic snapshot capabilities of btrfs and led me to look up what, if any, limits might apply. I find some threads from a few years ago that talk about limiting the number of snapshots for a volume to 100. The reason I'm curious is I wanted to try and use the snapshot capability as a way of keeping a 'history' of a backup volume I maintain. The backup doesn't change a lot overtime, but small changes are made to files within it daily. The Plan 9 OS has a nice archival filesystem that lets you easily maintain snapshots, and has various tools that make it simple to keep a /snapshot/yyyy/mmdd snapshot going back for the life of the filesystem. I wanted to try and replicate the basic functionality of that history using a non-plan-9 filesystem. At first I tried rsnapshot but I find its technique of rotating and deleting backups is thrashing the disks to the point that it can't keep up with the rotations (the cp -al is fast, but the periodic rm -rf of older snapshots kills the disk). With btrfs I was thinking perhaps I could more efficiently maintain the archive of changes over time using a snapshot. If this is an awful thought and I should just go away, please let me know. If the limit is 100 or less I'd need use a more complicated rotation scheme. For example with a layout like the following: min/<mm> hour/<hh> day/<dd> month/<mm> year/<yyy> The idea being each bucket, min, hour, day, month, would be capped and older snapshots would be removed and replaced with newer ones over time. so with a 15-minute snapshot cycle I'd end up with min/[00,15,30,45] hour/[00-23] day/[01-31] month/[01-12] year/[2018,2019,...] (72+ snapshots with room for a few years worth of yearly's). But if things have changed with btrfs over the past few years and number of snapshots scales much higher, I would use the easier scheme: /min/[00,15,30,45] /hourly/[00-23] /daily/<yyyy>/<mmdd> with 365 snapshots added per additional year.
