I have a VMFS volume that is made up of 3 800GB LUNs and hosting almost 90 VM's. The 8 hosts are currently running ESX 3.5 U2 with the VCenter server running 2.5 U5. We are planning to upgrade to ESX4 this year. What would be the ramifications of increasing the size of any or all of the LUNs on the datastore and running VMs? For example, if I only chose to grow the "middle" extent from our SAN management environment, would the VM's keep running and would the extra capacity be visible within the datastore? Most of these VM's are production and I don't want to do anything that could damage them.
Steve Hurd, MCSE, CCNA, VCP3
Floyd Memorial Hospital
New Albany, IN
You can not grow an ESX 3.x LUN, however you can with ESX 4. If there is anyway you can do it (not knowing the reasons for using extents) I would try and move away from extents unless you are using it specifically to try and get deeper storage q's.
I would avoid trying to do any sort of growth on an extent member, extents exist to grow datastores. I don't think they were ever designed to grow the LUN's used to grow the VMFS (via extents). It you must you extents, present the new storage as a LUN and add as an extent. However as already said I would try and move away from extents.
Check out Chad's blog for some good information http://virtualgeek.typepad.com/virtual_geek/2009/03/vmfs-best-practices-and-counter-fud.html
Basically don't use them unless you really know why you are doing it.
While preparing for the VCP4 exam I found this in the ESX config guide, pg 106, about ways to increase the size of a VMFS datastore:
Grow an extent in an existing VMFS datastore. Only extents with free space immediately after them are
expandable. As a result, rather than adding the new extent, you can grow the existing extent so that it fills
the available adjacent capacity.
Since we don't have any LUNS that have free space after them we wouldn't be able to grow the extents. We are planning to move to a new SAN in the next few weeks, so we'll address the sizing then.
Thanks to everyone for their help!