See the Problem FAQ for commonly-encountered problems and solutions.If that page doesn't help you, try asking on IRC or the Btrfs mailing list.To see if this is the case, first look for the amount of allocated space with If this shows the "used" value equal to the "total" value on each device, then everything has been allocated, which is the first condition for this problem.Secondly, look at the amount of space you have in metadata, as reported by If the "used" metadata is close to the "total" value, then that's the second condition for this problem, and you should read on. If the free space in metadata is less than or equal to the block reserve value (typically 512 Mi B, but might be something else on a particularly small or large filesystem), then it's close to full.If you have full up metadata, and more than 1 Gi B of space free in data, as reported by btrfs fi df, then you should be able to free up some of the data allocation with a partial balance: We know this isn't ideal, and there are plans to improve the behavior.Running close to empty is rarely the ideal case, but we can get far closer to full than we do. skip it If you see something like this when mounting: then you should run btrfs check on your fs.id=74101 The bug would only happen after some time, so I was able to move a lot of data onto the fs before btrfs crashed, and then it was just a case of unmounting and mounting again.Yes, the obviously critical fixes get to the latest stable kernel and sometimes get also applied to the long-term branches.
Before btrfs check I also resized the fs to smaller than it was and then to the max size using btrfs fi resize, which may have helped part way, but until I ran btrfs check, Data would not resize. When you haven't hit the "usual" problem If the conditions above aren't true (i.e.You need to mount file system with noatime flag to prevent this from happening. However COW will still be maintained for existing files, because the COW status can be modified only for empty or newly created files.More details are in Mount_options#Performance Renames NOT overwriting existing files do not give additional guarantees. For an empty file, add the NOCOW file attribute (use chattr utility with C), or you create a new file in a directory with the NOCOW attribute set (then the new file will inherit this attribute).there's plenty of unallocated space, or there's lots of unused metadata allocation), then you may have hit a known but unresolved bug.If this is the case, please report it to either the mailing list, or IRC.