On 2017-12-04 09:10, Duncan wrote:
Austin S. Hemmelgarn posted on Mon, 04 Dec 2017 07:18:11 -0500 as
excerpted:
On 2017-12-01 16:50, Matt McKinnon wrote:
Well, it's at zero now...
# btrfs fi df /export/
Data, single: total=30.45TiB, used=30.25TiB
System, DUP: total=32.00MiB, used=3.62MiB
Metadata, DUP: total=66.50GiB, used=65.16GiB
GlobalReserve, single: total=512.00MiB, used=0.00B
GlobalReserve seems to be used temporarily for certain cases of metadata
COW regardless of how full the FS actually is, I'm betting that it just so
happened that such a case was in progress when you got the info
previously. If you aren't seeing it regularly used, it's (probably) not
an issue.
Duncan is correct though when dealing with long-term usage. If you see
GlobalReserve usage that persists for an extended period of time,
something is almost certainly wrong, especially if the FS isn't close to
being full.
Thanks. I wasn't aware global reserve was routinely temporarily used.
I don't know that it's 'routinely' used, but I've seen it used
temporarily during balance and defrag runs, and on rare occasion when
snapshotting very subvolumes.
I'm pretty certain that all those cases are not 'supposed' to happen,
they just do as a consequence of how the code is written.
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