Tuesday, December 18, 2012

vSphere Boot Options

SD/USB requires setup of separate scratch area in shared storage to have persistent logs and crash dumps.  This is an additional configuration step and needs to be remembered and documented.  Personally, I do not recommend SD/USB, as maintenance of this infrastructure does not align well with established server administration methods.

BFS(Boot from SAN) is great for large environments, where generally there is an experienced SAN administrator and they are able to maintain the BFS infrastructure.  BFS gives you wonderful flexibility, as the blades themselves keep no state other than BIOS settings.  In addition, there is a considerable saving in eliminating 2 physical local disks from each ESXi server.  If you have 200+ of these servers then this is significant capex that is eliminated.  The cost of shared storage allocated for BFS is insignificant, as this is only ~6 GB of RAID5 storage per host.

Also note that BFS is not an option when your shared storage is NFS only (e.g. NetApp arrays).

BFS from iSCSI arrays is possible with hardware initiators, but it rather complex to set up and maintain, so it does not mesh very well with the small scale of typical iSCSI installations and the way they are operated.

So, BFS is really mainly for FC SAN.

On the other hand, the mirrored pair of local disks is very simple to set up and the boot from it is very simple to maintain.  All server administrators are familiar with it.  It nicely decouples the boot problems from the configuration of shared storage.  I generally recommend this setup for smaller environments, especially the less sophisticated ones, where there may not be a specialized SAN administrator.  The simplicity of management compensates for increased capex.

So my rules of thumb are very simple:

·         Auto-deploy                     - no, too complex for little benefit compared with BFS
·         SD/USB                                             - no, too awkward to maintain
·         Mirrored local disk          - yes, for small unsophisticated environments and where shared storage is NFS or iSCSI
·         BFS                                      - yes, for large environments with FC shared storage and good FC SAN skills

copied from a colleague :)