[DRBD-user] clarification about disable_sendpage parameter

Luca Lesinigo luca at lm-net.it
Sun Sep 4 22:02:40 CEST 2011


Documentation and website[*] tell that it is "recommended" to turn on disable_sendpage when running in a Xen Domain-0.

I seem to remember it was mainly an issue when running in active-active mode, and I'm sure my systems (active/passive) are running without that option since years without apparent problems.

I'd like to know if that recommendation is still relevant (drbd >= 8.3.9, linux >= 2.6.38, xen >= 4.1) and how it affects drbd.
I'm guessing it would just lower performance a little under normal conditions?
When running under Xen, is it actually _required_ or just recommended? and it's just for dual primary setups or even for the usual one way active/passive?
What problems could we see if we don't disable_sendpage in such environments?

Does that apply only when you run VM's directly off drbd (like some setups described on the net, maybe with the use of clustering solutions like pacemaker) or even when it's just an intermediate step (for example, my usual setup is disks > drbd > lvm2 in dom0, and domU running off logical volumes)?

[*] http://www.drbd.org/users-guide/s-xen-drbd-mod-params.html

Thanks,
--
Luca Lesinigo
LM Networks Srl



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