Re: Sharing a physical partition and ENBD?

[email protected] wrote:
> Hi!
> 
> I'm building a cluster based on RedHat Cluster Manager. This software 
> requires a small (20-30MB) shared device that both (or all) servers can 
> access simoultaneously. The software uses raw devices, so there is no 
> filesystem on that device (or the software manages reads & writes). The 
> software can actually use two shared devices, but the other is just a 
> backup.
> 
> My idea was to use a small partition on a local disk and export it to ENBD 
> - the cluster manager software on the first server would then use that 
> physical partition, which would also be exported to ENBD and used by the 
> other server.
> 
> On the second server, I would do the same - however it's physical 
> partition and it's ENBD export would be used as a 2nd (backup) shared 
> device.
> 
> Does that sound possible?

Well, bear in mind that changes made to the export on server A
without initiating them from the client on server B will not be seen by
the kernel on server B unless that kernel does absolutely NO caching!
I.e. it reads data anew without cconsulting its own buffers every time
it neeeds to know something.

Can you guarantee that? It sounds like you can, since you are using
serial access.

There is still a danger of races between two kernels to write the same
stuff, but maybe your softare can hande that. It would only require a
single common lock.


Peter