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Re: btrfs-cleaner frequently stuck at 100% CPU after 6.4.0 upgrade
After rebooting (pulling the cable, power-down-button had no effect) the system welcomed me with "Resyncing started for Volume data".
After that it was quite busy (15-min-load went up to 8.1, kworker using 90% CPU), later it was mainly the processes systemd-journal, md127_resync and md127_raid1. About 6 hours later load was back at 0.3, no process taking more CPU than usual.
The admin page no shows all used space as "data" (no space used by "snapshots", but as there is not much change in the data, the - existing - snapshots may take not much space).
So far: Looks good, thanks Netgear.
What I'd like to know: What was the problem? And which "rare" circumstances led to the complete inaccessibility of the device?
It seems like I found a way to get rid of the hanging btrfs-cleaner: After switching off quota
btrfs quota disable /data
btrfs-cleaner did never show up again (in top).
Hi Hans,
like you, I haven't enabled quota myself and they're not used in any of my shares.
I would've tried the "quota disable" command if it had been obvious whether it destroys all of the qgroups on the volume (visible using "qgroup show /data"). Is this documented anywhere for btrfs?
It's also not clear how to re-enable quota if it requires re-creating all the qgroups as described on the wiki. Is it documented anywhere how ReadyNAS OS requires qgroups to be set up?
In the end, by the time I got access to my NAS 6.4.1-T21 beta was out, so I installed it and haven't had problems since (after 10h of uptime, btrfs-cleaner is still below 7s of CPU time). So I'll consider this fixed if the beta ever turns into a release.
Re: btrfs-cleaner frequently stuck at 100% CPU after 6.4.0 upgrade
I see a similar issue, but not matching the descriptions exactly. In my case, top doesn't show btrfs-cleaner using 100% CPU, but if I install iotop, I see the process eating all of the available disk IO, meaning that most of the CPU is spent in iowait. This causes any other disk-bound process to run extremely slowly; I see similar usability symptoms as others (slow FrontView response, failed NAS mounting, file reads, etc).
This has been persistent under 6.4.0 and the latest 6.4.1 RC3 (running RC3 and observing this as I type):
Total DISK READ: 759.25 K/s | Total DISK WRITE: 0.00 B/s
TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND
1938 be/4 root 381.48 K/s 503.70 K/s 0.00 % 97.83 % [btrfs-cleaner]
1939 be/4 root 374.07 K/s 500.00 K/s 0.00 % 96.80 % [btrfs-transacti]
