On Sun, 16 Oct 2016 15:03:24 +0800 William Josefsson wrote:
> Hi list, while I know that writes in the RADOS backend are sync() can
> anyone please explain when the cluster will return on a write call for
> RBD from VMs? Will data be considered synced one written to the
> journal or all the way to the OSD drive?
This has been answered countless (really) here, the Ceph Architecture
documentation should really be more detailed about this, as well as how
parallel the data is being sent to the secondary OSDs.
It is of course ack'ed to the client once all journals have successfully
written the data, otherwise journal SSDs would make a LOT less sense.
> Each host in my cluster has 5x Intel S3610, and 18x1.8TB Hitachi 10krpm SAS.
The size of your SSDs (you didn't mention) will determine the speed, for
journal purposes the sequential write speed is basically it.
A 5:18 ratio implies that some of your SSDs hold more journals than others.
You emphatically do NOT want that, because eventually the busier ones will
run out of endurance while the other ones still have plenty left.
If possible change this to a 5:20 or 6:18 ratio (depending on your SSDs
and expected write volume).
> I have size=3 for my pool. Will Ceph return once the data is written
> to at least 3 designated journals, or will it in fact wait until the
> data is written to the OSD drives? thx will
> ceph-users mailing list
Christian Balzer Network/Systems Engineer
ch...@gol.com Global OnLine Japan/Rakuten Communications
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