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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