[Beowulf] clustering using xen virtualized machines
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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