On Wed, Jul 18, 2018 at 12:36 PM Nikola Ciprich <nikola.ciprich@xxxxxxxxxxx> wrote:
;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?
What's the output from "rbd info nvme/centos7"?
> 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..
Odd. The exclusive-lock code is only executed once (in general) upon the first write IO (or immediately upon mapping the image if the "exclusive" option is passed to the kernel). Therefore, it should have zero impact on IO performance.
BR
nik
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