mshahamiri
Contributor
Contributor

Creating multiple VMFS volumes inside a big VMFS volumes

Hi all,

I have a general question. I am wondering what is the pros/cons of creating multiple VMFS volumes inside a VMFS volume. The reason that I am interested is that there are several virtual appliances that can present attached disks as iSCSI luns. To do that you need to first attach one or more disks to the virtual appliance (basically creating a disk for that virtual appliance on a VMFS volume). After that the virtual appliance will partition that disk and present a part of it to ESX server as an iSCSI lun. Then, I can add the iSCSI lun to storage (basically format it with VMFS). The bottom line is that I am creating one or multiple seperate VMFS volumes inside a big VMFS volume. Just wondering if that will cause any issue (I think it is clear that we might have some performance penalty but I am more concern about any potential problem rather than performance)

Thanks,

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8 Replies
paulmack
Enthusiast
Enthusiast

What do you want to do with the iscsi lun's? Run VM's on them? I use a setup similar to what you describe to present ISO's and templates to all our seperate clusters via an iscsi lun. Different clusters are in different storage goups on the SAN so using an iscsi lun from openfiler VM saved me a load of storage system work.

I think you would suffer greatly if you try to run VM's from it though.

Cheers

Paul

krowczynski
Virtuoso
Virtuoso

Generally it is better to have more smaller LUN#s for better Performance.

You should not have more than 10 vm located on an LUN.

MCP, VCP

MCP, VCP3 , VCP4
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RahulMM
Enthusiast
Enthusiast

ESX can easily manage 256 VMFS partition and LUNs, it is not considered best practice to use extents for your VMFS partitions.

you can add extents to the LUN. Each LUN is limited to 2TB. Each VMFS volume can have 32 extents. So your VMFS volume can be 64 TB's.

But you are running the risk of data loss, if you lose a LUN from your extent you have lost the entire VMFS partition or all your VM Guests. If you have four or five separate LUNs you will only lose the Guests on that particular LUN. (extents are similar to disks concatenation... so if you loose your first disk (or partition) you loose everything.)

I prefer to use different datastore... or if you simple extent a LUN on storage side, you can use the new grow mode to expand also the VMFS datastore. Edit

The adage here is just because you can do something, does not necessarily mean it is good to do so.

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mshahamiri
Contributor
Contributor

Thanks for reply

Yes, I want to put some VMs on the iSCSI

lun. I am ok with having some performance penalty on the VMs, but not

sure if that (creating VMFS inside a VMFS) cause any harm to VMFS/ESX

server or disturb some functionalities. Also you mentioned about

openfiler. How robust it is? have you tried to execute some VMware

functionalities like Vmotion, snapshot etc?

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dominic7
Virtuoso
Virtuoso

ESX can easily manage 256 VMFS partition and LUNs, it is not considered best practice to use extents for your VMFS partitions.

you can add extents to the LUN. Each LUN is limited to 2TB. Each VMFS volume can have 32 extents. So your VMFS volume can be 64 TB's.

But you are running the risk of data loss, if you lose a LUN from your extent you have lost the entire VMFS partition or all your VM Guests. If you have four or five separate LUNs you will only lose the Guests on that particular LUN. (extents are similar to disks concatenation... so if you loose your first disk (or partition) you loose everything.)

I prefer to use different datastore... or if you simple extent a LUN on storage side, you can use the new grow mode to expand also the VMFS datastore. Edit

The adage here is just because you can do something, does not necessarily mean it is good to do so.

I wouldn't say that ESX can "easily" handle 256 LUNs, but it can handle that many ( depending on how many paths there are to each lun ).

I'll also chime in on extents as what you posted above isnt' entirely true anymore. If you lose an extent to a VMFS ( in vSphere VMFS 3.31+ ) you can actually have a partial failure of the the VMFS volume where the only data that is lost is the data that was on the lost extent. Of course it's hard to tell what data would be on that extent, and I would agree that in general extents aren't particularly awesome for most cases.

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DSTAVERT
Immortal
Immortal

There are several Virtual Appliances and many software packages that do just that. You basically create an iSCSI VM and assign it all the local disk space or??. You then add the iSCSI LUN as a datastore to the ESXi host. Now you create all your VM inside this iSCSI datastore. HP has a virtual Lefthand SAN appliance, Openfiler, etc do as well

-- David -- VMware Communities Moderator
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paulmack
Enthusiast
Enthusiast

I've only run VM's via iscsi from openfiler in my test rig. Which consists of ESX VM's, VC VM and openfiler VM all running in Workstation on my laptop. I did successfully VMotion VM's in this environent. I've not run any VM's from openfiler in my production environment. Like I said I only use this for ISO storage and presentation in production but I can't really see any reason other than perormance why openfiler wouldn't be able to provide you what you want.

Cheers

Paul

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mshahamiri
Contributor
Contributor

Thanks for replies,

so I guess nobody hit any weird issue, I am gonna try it out and see what will happen, as Paul mentioned I will start with the lab environment only.

--Masoud

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