Messages in this thread | | | Date | Fri, 15 Feb 2019 22:41:26 +0000 | From | "Richard W.M. Jones" <> | Subject | Re: nbd, nbdkit, loopback mounts and memory management |
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On Fri, Feb 15, 2019 at 08:19:54PM +0100, Pavel Machek wrote: > Hi! > > I watched fosdem talk about > nbdkit... https://www.youtube.com/watch?v=9E5A608xJG0 . Nice. But word > of warning: I'm not sure using it read-write on localhost is safe. > > In particular, user application could create a lot of dirty data > quickly. If there's not enough memory for nbdkit (or nbd-client or > nbd-server), you might get a deadlock.
Thanks for the kind words about the talk. I've added Wouter Verhelst & the NBD mailing list to CC. Although I did the talk because the subject is interesting, how I actually use nbdkit / NBD is to talk to qemu and that's where I have most experience and where we (Red Hat) use it in production systems.
However in January I spent a lot of time exercising the NBD loop-mount + nbdkit case using fio in order to find contention / bottlenecks in our use of threads and locks. I didn't notice any particular problems then, but it's possible my testing wasn't thorough enough. Or that fio only creates small numbers of dirty pages (because of locality in its access patterns I guess?)
When you say it's not safe, what could happen? What would we observe if it was going wrong?
> Also note that nbd.txt in Documentation/blockdev/ points to > sourceforge; it should probably point to > https://github.com/NetworkBlockDevice/nbd ?
Wouter should be able to say what the correct link should be.
Rich.
-- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://libguestfs.org
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