When we do a boot from SAN for Linux, it's simple, we choose Linux. When we do a boot from SAN for Windows, it simple as well, we choose Windows (Windows_2008 or GPT depending on the version)
When we do a boot from SAN for ESX, we could choose:
- Linux: because it's a Linux-like OS with Linux-like partitions, and it seems to fit well.
- VMWARE: because it's VMWARE. But there is an issue doing this: VMWARE lun type has a good alignment for VMFS datastores and I don't think system luns use the same alignement than datastores. And Dan and Keitha confim there is misalignment seen when using vmware lun type.
The question is which choice is better and an official statement somewhere in NetApp docs would really be great.
off topic:
- About the impact of alignment on system luns, I agree with Keitha: there is nearly no I/Os on system luns for ESX so there should be little to no impact on the aggregate. If disks have to work twice as hard for near-zero I/Os, there is no real problem.
- Doug, you are right, misalignment on VMware can be a real pain, but it usually occurs because of misaligned vmdks on datastores (very often caused by a bad P2V conversion) or by a bad lun type for RDM luns. It's never an issue coming from the system luns.
That why every administrator should pay attention to vmdk alignement and use mbralign tool when necessary or, if VMs cannot be stopped, use the new feature from the VSC to create a misaligned datastore, so the misaligned vmdks become aligned with ONTAP luns: the same way system luns don't produce a lot of I/Os, datastore don't produce a lot of I/Os. Most of I/Os come from vmdk, that why these have to be aligned.
- And finally when there is such misalignment issue, it only has a real impact when the aggregate is already under heavy load, and Cache and NVRAM can't hide the problem anymore.
(BTW, be careful in reading ONTAP CLI report for alignments: partial reads on RDM Log luns don't mean there is alignment issue for example, but they are often seen as unaligned ).
