My mnemonic is “In Essence” and “for EGsample”

soft keyword for anyone not familiar like I was ...

"A new soft keyword lazy is added. A soft keyword is a context-sensitive keyword that only has special meaning in specific grammatical contexts; elsewhere it can be used as a regular identifier (e.g., as a variable name). The lazy keyword only has special meaning when it appears before import statements..."

I've been using btrfs for maybe 10 years now? -- on a single Linux home NAS. I use it in a raid1c3 config (I used to do c2). raid1cN is mirroring with N copies. I have compression on. I use snapshots rarely.

I've had a few issues, but no data loss:

* Early versions of btrfs had an issue where you'd run out of metadata space (if I recall). You had to rebalance and sometimes add some temporary space do that.

* One of my filesystems wasn't optimally aligned because btrfs didn't do that automatically (or something like that -- this was a long time ago.) A very very minor issue.

* Corruption (but no data loss, so I'm not sure it's corruption per se...) during a device replacement.

This last one caused no data loss, but a lot of error messages. I started a logical device removal, removed the device physically, rebooted, and then accidentally readded the physical device while it was still removing it logically. It was not happy. I physically removed the device again, finished the logical remove, and did a scrub and the fsck equivalent. No errors.

I think that's a testament to its resiliency, but also a testament how you can shoot yourself in the foot.

I've never used RAID5/6 on btrfs and don't plan to -- partly because of the scary words around it, but I also assume the rebuild time is longer.

I think of this as fail fast. Fail immediately so its easy to root cause the failure and not have it be hidden and cause more obscure side effects later.