ESXi and LUNs

[danilodicesare]

Hi all,

i've got a discussion with a colllegue of mine regarding LUN owned from different ESXi servers.

Do you think is a good idea to share all lun on all ESXi server (so i'll have a big SAN zoning) even if ESXi server are not 'clustered'?

How the lock on VMFS works?

I do prefer (but i may be wrong) to use shared LUN only in a Cluster ESXì environment......

what do you think guys?

tnx

Dan

[idle-jam]

i prefer your suggestion as it does not make sense to be accessible by non cluster (afterall you can't vmotion). but sometimes if you just want to shared the storage across and that you do not care about management then it make sense too. how many LUNs do you have and hosts do you have?

[danilodicesare]

Hi,

i've got 32 server and 20 TB of spaces and a lots of LUNs.....

what happens if 2, 3 or 4 ESXi not clusterd have access to same shared LUN?

tnx

dan

[idle-jam]

a file lock will enable on each of the VM with .lck extension (when powered up on a host). so when another host try to register the VM to power up it will not work.

[danilodicesare]

yes,

ok for VM lock but arbitration beetwen host are done?

do you think is best practise to have all lun shared and a big zone on SAN?

vMotion and Storage vMotion will work only if a ESXì are clustered and if all ESXi share the same SAN zoning (so one zone for all ESXi)

tnx

dan

[MauroBonder]

you can read this document, there expalain how VMFS works. http://www.vmware.com/files/pdf/VMware-vStorage-VMFS-DS-EN.pdf

[marcelo_soares · Accepted solution]

The main questions here are:

- Do you have vmotion enabled for this ESX's?

- Do you have VMs on a same datastore running on different ESX's?

If yes to any, you can and should share the LUN's accross ESX's. Even if you don't have vCenter, you will be able to take advantage on manual failovers, for example, in case one of your ESX fails.

The ESX (until version 4.x and on storages that don't support VAAI on 4.1) uses LUN reservation when they need to change VMFS metadata, meaning information on file timestamps, file size, and permissions to erase/change/create file information. This reservation makes the LUN unavailable for all other ESX's that are using the colume in a given moment (very short, miliseconds depending on your SAN speed). So, more ESX's you have accesing VMs on a specific datastores, more conflicts you'll have.

The KB http://kb.vmware.com/kb/1002293 talks a bit more about it.

[danilodicesare]

Hi Marcelo,

have you got any link about technical explanation about lock and behaviour of VMFS and storage with and without VAAI?

tnx again

Danilo

[marcelo_soares]

Not really. I never had a chance to test VAAI deeply. You can check the default VMware manuals and google it. Some of them:

http://www.vmware.com/pdf/vsphere4/r41/vsp_41_esx_server_config.pdf

http://www.vmware.com/pdf/vsphere4/r41/vsp_41_san_cfg.pdf