On 27 Jul 2017 6:11 pm, "Gionatan Danti" <[email protected]> wrote:
Il 27-07-2017 09:38 Gionatan Danti ha scritto: > > Thanks for your input. I also read your excellent suggestions on link > Igor posted. > > To clarify: the main reason I am asking about the feasibility of a dual-primary DRBD setup with LVs on top of it is about cache coherency. Let me do a step back: the given explaination for deny even read access on a secondary node is of broken cache coherency/consistency: if the read/write node writes something the secondary node had previously read, the latter will not recognize the changes done by the first node. When in cluster mode LVM will not use local cache that's part of the configuration you need to do during setup. The canonical solution to this problem is to use a dual-primary setup with a clustered filesystem (eg: GFS2) which not only arbitrates write access, but maintains read cache consistency also. Now, let's remove the clustered filesystem layer, leaving "naked" LVs only. How read cache coherency is mantained in this case? As no filesystem is layered on top of the raw LVs, there is not real pagecache at work, but the kernel's buffers remains - and they need to be made coherents. How DRBD achieves this? Does it update the receiving kernel I/O buffers each time the other node writes something? Thanks. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: [email protected] - [email protected] GPG public key ID: FF5F32A8 _______________________________________________ drbd-user mailing list [email protected] http://lists.linbit.com/mailman/listinfo/drbd-user
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