RAW LUNS (Direct to LUN) and VMs

[jdamnation]

Hi all,

First post and that...

Looking at the WIKI there is a statement about how it is 'Dangerous' to use Direct to LUN mappings (aka 'RAW LUN') with VMs. Something about the fact that Proxmox does not remember when you have used a LUN in a direct map and thus it's possible for you to select the same LUN later on and thus have problems.

So what I was wanting to know - is - is this still the case?

If so - is there any feature planned in the roadmap that might put a star next to a LUN that had already been mapped - and perhaps even - the name of the VM which was using it in brackets?

Cheers,

JD

 

[dietmar]

The suggestion is to use LVM (that way we can add marks (lv names)).

 

[jdamnation]

Really!? Use LVM just because you can't change the name / keep tabs on RAW mappings usage?

How does using LVM effect things like performing resizing the LUN on the SAN? With a RAW device map you can just edit the LUN size on the SAN and boom - you have a larger LUN. Surely with LVM this is not so easy? We would generally use one LUN per VM guest - I'm not really very familiar with the 'considerations' of using LVM - are there any? Are there any guides / best practice info on LVM with Promox.

 

[dietmar]

Really!? Use LVM just because you can't change the name / keep tabs on RAW mappings usage?

The idea is to define one big lun, and manage everything using LVM.

 

[jdamnation]

OK that's a huge flaw IMHO.

If you are using an advanced SAN, you want to snapshot each LUN independently. Perhaps some LUNs are more important than others and thus you need to snapshot them more than others. Also you might want to DR certain more important LUNS using the SAN than others.

So sticking everything on the same LUN on your SAN isn't making the best of your SAN I'm afraid.

Really would be good for Proxmox to be able to 'label' Raw Device Mappings and to simply tell you when one has been used.

That would be a massive improvement in my book.

Cheers,

JD

 

[tom]

the storage model is flexible, you can do what you want. but LVM is really nice, but if you do not want to use it you do not have to.

 

[jdamnation]

Well it was just the clear indication in the wiki that you should not use Raw Device Mappings with Proxmox as it's 'DANGEROUS'.

When I read that something is dangerous - I don't do it.

Therefore I have to assume that you should not use Raw Device Mappings with Proxmox - which is a deal breaker - for us at least - for the reasons I have stated above.

JD