Originally posted by jlittle
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The problem has always been that snapshots eventually fill up if left alone, and when their combined total size, plus the operating system size, goes over 90% the performance begins to suffer, and so do maintenance tools like balance, scrub, check and others.
When I first started using BTRFS over five years ago I went snapshot wild, creating 50-100, along with pre and post package updates. I never got to the 90% threshold but I began to wonder, as I looked at the older snapshots, "what am I keeping them for?" Why would I ever revert to a snapshot that is a month old, much less a year old, or older? I thought of all the data I'd lose reverting to an old snapshot -- emails, calendar data, app installs, DE customizations, code I'd written, etc... Had I upgraded my distro version why would I want to revert to the previous or older version in an old snapshot?
That's when I started copying data I wanted to keep long term, like my wife's genealogy and family tree data, my old coding (SAVVY, Turbo Pascal 3.02A, Pascal), my math and physics documents, etc., to multiple external disk drives as themselves, without using any intervening technology like BTRFS. That data never changes. It is like a photo of my family hanging on the wall. But, I have that data on my current system as well, for occasional reference and trips down memory lane. The TP302A files date from June of 1992, and my Lotus AmiPro spreadsheets (.SAM) that I used to invoice my clients date from before that.
I've had clients that generated data and documentation that laws required they keep for 15 years. That data was printed out on paper and stored in indexed cardboard boxes which were stacked six high in warehouses. When some lawyer wanted a certain document a gofer was sent over to retrieve it and make a photocopy of it, returning the original to the box. If you ran a spreadsheet written with Lotus Notes having a paper copy was/is the only reliable way to save that data. Think where they'd be if they had stored their spreadsheet files on Zip drives. Fifteen years later the drives don't work and Lotus Notes died long ago. That spreadsheet data is lost for good. I keep my .SAM spreadsheets on the hope that someone will make a converter for them.
For my use case BTRFS is perfect: quick and easy to use. I limit my snapshots to around 5 for my only subvolume, @. I always do a snapshot before I run an update and full-upgrade. If things don't go well I can roll back quickly. No harm, no foul. If after I check my WINE apps, virtual machines, my Jupyter Notebooks, and my steam games and everything runs well I will create a new snapshot. I always delete the oldest snapshot when I create a new one, maintaining the 5 snapshot count. I always plug in my 500Gb USB SSD drive when running make_snapshots.sh to keep a "take with me copy" of my Neon installation. I have a 1Tb NVMe SSD also labeled "BACKUP" and when my USB SSD, which is labeled "BACKUP" as well, is not plugged in the mount command in my script mounts the NVMe.
PS - My use case is testing distros in VM's, creating Jupyter Notebooks to test Covid and other data for validity, emailing friends and relatives, shopping online, keeping up with news and weather, visiting KubuntuForums.net and other websites, and playing games locally, mainly Minecraft. Simple uses. One nice feature of BTRFS is that I can navigate through a snapshot and pull out files and folders as if they were on an EXT4, or C:/ drive, or what ever.
What am I missing or not seeing? 
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