[ceph-users] read performance, separate client CRUSH maps or limit osd read access from each client

Martin Verges martin.verges at croit.io
Thu Nov 8 23:21:07 PST 2018


Hello Vlad,

Ceph clients connect to the primary OSD of each PG. If you create a
crush rule for building1 and one for building2 that takes a OSD from
the same building as the first one, your reads to the pool will always
be on the same building (if the cluster is healthy) and only write
request get replicated to the other building.

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2018-11-09 4:54 GMT+01:00 Vlad Kopylov <vladkopy at gmail.com>:
> I am trying to test replicated ceph with servers in different buildings, and
> I have a read problem.
> Reads from one building go to osd in another building and vice versa, making
> reads slower then writes! Making read as slow as slowest node.
>
> Is there a way to
> - disable parallel read (so it reads only from the same osd node where mon
> is);
> - or give each client read restriction per osd?
> - or maybe strictly specify read osd on mount;
> - or have node read delay cap (for example if node time out is larger then 2
> ms then do not use such node for read as other replicas are available).
> - or ability to place Clients on the Crush map - so it understands that osd
> in - for example osd in the same data-center as client has preference, and
> pull data from it/them.
>
> Mounting with kernel client latest mimic.
>
> Thank you!
>
> Vlad
>
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