;6QHi Janon,
> Just to clarify: modern / rebased krbd block drivers definitely support
> layering. The only missing features right now are object-map/fast-diff,
> deep-flatten, and journaling (for RBD mirroring).
I thought it as well, but at least mapping clone does not work for me even
under 4.17.6:
[root@v4a ~]# rbd map nvme/xxx
rbd: sysfs write failed
RBD image feature set mismatch. You can disable features unsupported by the kernel with "rbd feature disable nvme/xxx".
In some cases useful info is found in syslog - try "dmesg | tail".
rbd: map failed: (6) No such device or address
(note incorrect hint on how this is supposed to be fixed, with feature disable command without any feature)
dmesg output:
[ +3.919281] rbd: image xxx: WARNING: kernel layering is EXPERIMENTAL!
[ +0.001266] rbd: id 36dde238e1f29: image uses unsupported features: 0x38
[root@v4a ~]# rbd info nvme/xxx
rbd image 'xxx':
size 20480 MB in 5120 objects
order 22 (4096 kB objects)
block_name_prefix: rbd_data.6a71313887ee0
format: 2
features: layering
flags:
create_timestamp: Wed Jun 20 13:46:38 2018
parent: nvme/centos7@template
overlap: 20480 MB
is trying 4.18-rc5 worth giving a try?
> If you are running multiple fio jobs against the same image (or have the
> krbd device mapped to multiple hosts w/ active IO), then I would expect a
> huge performance hit since the lock needs to be transitioned between
> clients.
nope, only one running fio instance, no users on the other node..
BR
nik
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