Hi Janek,
this 'ceph features' output that you're probably referring to (or maybe
'ceph tell mon.X sessions') comes up every now and then, for example [0],
[1], [2]. I also still don't have a definitive answer, unfortunately. But
from my understanding those are compatibility features that don't
necessarily reflect the actual ceph version. For example, I have a test
cluster with tentacle:
tentacle:~ # ceph versions
{
"mon": {
"ceph version 20.2.0 (69f84cc2651aa259a15bc192ddaabd3baba07489)
tentacle (stable - RelWithDebInfo)": 1
},
"mgr": {
"ceph version 20.2.0 (69f84cc2651aa259a15bc192ddaabd3baba07489)
tentacle (stable - RelWithDebInfo)": 2
},
"osd": {
"ceph version 20.2.0 (69f84cc2651aa259a15bc192ddaabd3baba07489)
tentacle (stable - RelWithDebInfo)": 3
},
"mds": {
"ceph version 20.2.0 (69f84cc2651aa259a15bc192ddaabd3baba07489)
tentacle (stable - RelWithDebInfo)": 1
},
"overall": {
"ceph version 20.2.0 (69f84cc2651aa259a15bc192ddaabd3baba07489)
tentacle (stable - RelWithDebInfo)": 7
}
}
but 'ceph features' shows squid:
tentacle:~ # ceph features
{
"mon": [
{
"features": "0x3f07fffffffdffff",
"release": "squid",
"num": 1
}
],
"mds": [
{
"features": "0x3f07fffffffdffff",
"release": "squid",
"num": 1
}
],
"osd": [
{
"features": "0x3f07fffffffdffff",
"release": "squid",
"num": 3
}
],
...
And this cluster also has "luminous" clients connected although I enforced
"squid" with 'ceph osd set-require-min-compat-client squid'. In our
production cluster I haven't enforced that, it is still running with
luminous as min-compat-client because we actually do have a couple of older
clients and don't want to risk anything, but we're going to have to deal
with them at some point.
Anyway, I'm not recommending to enforce the require-min-compat-client
update, I'd rather suggest to set up a test cluster with a couple of your
typical clients maybe, and then see if they successfully connect. I did the
same in my lab virtual environment that resembles our prod. cluster
(OpenStack with Ceph), there I enforced "reef" as min-compat-client and new
mounts from Ubuntu machines (24.04, kernel 6.8.0) with Ceph 19.2.1 packages
still report luminous on a CephFS mount. But the mount works, so I assume
that everything is okay in the lab. But I'm still not feeling confident
enough to recommend you to update it. ;-)
Hopefully someone else chimes in and contradicts or confirms my
statement(s).
Regards,
Eugen
[0]
https://lists.ceph.io/hyperkitty/list/[email protected]/thread/A4IWXINDBM6KI4DJXC62TNE2Y37P2EM2/#36GQ5PJ74JIYUGTS2SSVYBXKIQF7WRN5
[1]
https://lists.ceph.io/hyperkitty/list/[email protected]/thread/RVND3Y3Z7FDR4ENHKOSDHFJ5XBZJR547/#YKJPMWJAL7X4T4UIQ6JRYV2LKG6G2JND
[2]
https://lists.ceph.io/hyperkitty/list/[email protected]/thread/WSADGYBR7PLUBWSEBTJDKETU534R4FX4/#FNCJBSL7IB2HAQZPFWO4P6O6ELOMKYYX
Am Mi., 28. Jan. 2026 um 09:16 Uhr schrieb Janek Bevendorff via ceph-users <
[email protected]>:
> I just noticed that this applies to RBD clients as well. How is this
> supposed to work? Can you use only radosgw and ceph-fuse if you want to
> use upmap-read? It seems strange to me that the most central Ceph
> systems don't work with these new features.
>
>
> On 26/01/2026 18:55, Janek Bevendorff via ceph-users wrote:
> > Hi,
> >
> > Is there a way to use the new upmap-read balancer mode when I have
> > CephFS kernel clients connected? Our cluster runs Squid and all
> > connected clients are on kernel 6.11-6.14, so they should be new
> > enough. However, they identify themselves as luminous (I could not
> > find clear documentation about this, but this seems to be hard-coded
> > and by design), so I cannot run ceph osd set-require-min-compat-client
> > reef, which is required for the balancer module to work.
> >
> > I have 500 clients connected and migrating them all to FUSE would be a
> > headache. Is there a way around that? Some of my pools have extremely
> > high read balance scores and we're also struggling with performance
> > issues as a result.
> >
> > Janek
> >
> >
> > _______________________________________________
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>
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>
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