28 Jan
2020
28 Jan
'20
10:10 p.m.
On 1/28/20 7:03 PM, David DELON wrote:
Hi,
i had a problem with one application (seafile) which uses CEPH backend with librados.
The corresponding pools are defined with size=3 and each object copy is on a different
host.
The cluster health is OK: all the monitors see all the hosts.
Now, a network problem just happens between my RADOS client and a single host.
Then, when my application/client tries to access an object which is situed on the
unreachable host (primary for the corresponding PG),
it does not failover to another copy/host (and my application crashes later because after
a while, with many requests, too many files are opened on Linux).
Is it the normal behavior? My storage is resilient (great!) but not its access...
Yes. Reads and Writes for a PG are always served by the primary OSD.
That's how Ceph is designed.
If on the host, i stop the OSDs or change the affinity
to zero, it solves,
so it seems like the librados just check and trust the osdmap
And doing a tcpdump show the client tries to access the same OSD without timeout.
There is a network issue and that's the root cause. Ceph can't fix that
for you. You will need to make sure the network is functioning.
It can be easily reproduced with defining a netfilter rule on a host to drop packets
coming from the client.
Note: i am still on Luminous (both on lient and cluster sides).
Again, this is exactly how Ceph works :-)
The primary OSD serves reads and writes. Only when its marked as down
the client is informed using an osdmap update and then it goes to
another OSD.
Wido
>
> Thanks for reading.
>
> D.
>
>
>
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