EMC as a best practice recommends a Host be giving access to only one storage group however LUNs can be members of multiple storage groups, When booting from SAN the Host needs exclusive access to the Boot lun so for EXS clusters we must create storage groups for each host to contain the boot LUN and then add every lun that is a shared datastore into the storage groups as well to allow the Hosts to share access to them. When adding the Luns to the storage group they are given HostIDs, in a large dynamic cluster with multiple Host and a large number of datastores it is difficult to ensure that the HOST IDs match accross each Host. I have seen threads that suggest the HostID is only critical when using RDM luns, however the VShpere storage guide recommends keeping these IDs consistent.
1) should we make every effort to keep these IDs consistent accross each Host even if we are not supporting RDM's? With the latest versions of vShpere 5.0 / 5.1 is this not a big concern?
2) Any recomendations from an operational perpesctive to ensure during LUN provisioing that Host IDs added into storage Groups are consistent?
My personal experience is that it is better to keep the LUN ID consistent. Then if you need to re install ESXi you know without thinking which LUN it should be using because the ID is available in the details view of the installation screen. But there may be other factors or reasons why you might not.
thanks for the response. We are looking to use a storage group per ESX Host and we will pre-provision as much of the storage and hosts as possbile to ensure the LUNs are added to all storage groups at the same time and recieve the same Host ID's but we are concerned that future additions may be difficult to ensure the Host IDs match up. From all of our testing it appears that if Datastores do not have the same Host ID accross ESX Host all cluster functionailty seems to be in tact, so we are just trying to find out if there other any other issues outside of RDM's that we should be concerned of regarding mis matched Host ID's for some LUNs.
You should look into the caveats around replication. Our on site EMC guru pushed very hard for consistent Lun ids, there must be very good reasons why.
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