[Beowulf] clustering using xen virtualized machines

Tim Cutts tjrc at sanger.ac.uk
Tue Jan 26 06:24:20 PST 2010

On 26 Jan 2010, at 1:24 pm, Tim Cutts wrote:

> 2)  Raw device maps (where you pass a LUN straight through to a  
> single virtual machine, rather than carving the disk out of a  
> datastore) reduce contention and increase performance somewhat, at  
> the cost of using up device minor numbers on ESX quite quickly;  
> because ESX is basically Linux, you're limited to 256 (I think - it  
> might be 128) LUNs presented to each host, and probably to each  
> cluster, since VMs need to be able to migrate.  I basically use RDMs  
> for database applications where the storage requirements are greater  
> than about 500 GB.  For less than that I use datastores.

It's been pointed out to me that of course Linux supports a lot more  
than 256 devices presented.  Nevertheless, for some reason ESX does  
not - presumably it's only using a single major number or something.


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