LUN to VM and Host Ratio

Posted on 2013-02-06
Last Modified: 2016-11-23
We are currently planning to virtualize our physical environment. We have purchased a dell equallogic PS4100X (iscsi) with 24 x 600GB SAS disks which will be configured in a RAID 50 Configuration with two hot spares. Total usable storage will be approx 13 TB.

We will be running Vsphere 5.1 essentials plus across two Physical Vmware hosts.

15 physical servers will be virtualized and another 5 servers will be deployed over the next 3 months.

Our current data storage usage is 2TB and approx storage to be used up after virtualization will be approx 3 TB.

We are planning to dedicate a LUN for disk backups (before spinning off to tape)

Initally we were thinking of have two luns and two datastores. One for production servers and the other as the backup storage area However after some research we have some concerns if this will impact performance.

After reading a best practice white paper from vmware it was recommended to have a "consolidation with some level of isolation"

Our servers are not very resource hungry we have a typical windows environment with  file servers, DCs, SQL 2005, 2 x citrix servers with approx 60 citrix users and Exchange.

As a rough guideline how many LUNS per VM should we have? What whould we be considering?

Is there an issue with two vm hosts accessing the same datastore/LUN ?

I think we should carve out LUNs as required so maybe we should start with 2 or 3 LUNs and spread our servers across there then create additional LUNs as required.

any advice would be appreciated.
Question by:BA-IT-2000
LVL 118

Accepted Solution

Andrew Hancock (VMware vExpert / EE MVE) earned 250 total points
ID: 38862987
We prefer smaller LUNs to larger LUNs, just because of disaster recovery, larger the LUN, you can have more VMs, but if there is a disaster with a LUN failure you loose more VMs.

we work on 5-6 VMs per LUN, and create LUNs between 500-800GB. Unless we require a supersized LUN for specific VM.

There is no issue with multiple ESXi hosts accessing the same LUN.

We also spread the VMs across LUNs, so we do not put all our DCs on the same LUN, same with SQL servers, Exchange servers, spread them across LUNs.

Assisted Solution

xperttech earned 250 total points
ID: 38865801

Just to clarify, VMs are not traditionally assigned LUNs directly. It is possible but usually we try to avoid that. Mapping LUNs directly to VMs is called RDM (Raw Disk Mapping). VMs usually get virtual disks (VMDKs).

When you present a LUN to your VMware hosts, the first one to map it will format it with the VMFS filesystem. This format allows for multiple host access (read/write). This is VMware's filesystem as opposed to NTFS from Microsoft where you cannot have more than one host reading the LUN unless you are using clustering technology. The rest of the ESXi hosts will see the new VMFS and also map it. For DRS (distributed resource scheduler) and HA (high availability) to work properly, shared storage is key.

Hanccocka already answered above the recommendation about sizing and this coincides with my experience too.

Once a LUN is formatted with VMFS, it becomes a datastore. You can have your local datastores and your shared datastores.

What VMware admins need to do when deploying VMs is find a balance in performance and sizing when selecting among multiple datastores (shared storage).

When you create a new VM and select a datastore, the host creates a folder with your VM's name and there it places the files that make up your VM. See here the different files you can find there. The key files are VMDK (virtual disks) and VMX (your VM config descriptor file), but there are many there...

Hope this helps....

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Moving your enterprise fax infrastructure from in-house fax machines and servers to the cloud makes sense — from both an efficiency and productivity standpoint. But does migrating to a cloud fax solution mean you will no longer be able to send or re…
Will try to explain how to use the VMware feature TAGs in the VMs and create Veeam Backup Jobs using TAGs. Since this article is too long, I will create second article for the Veeam tasks.
This video teaches viewers how to encrypt an external drive that requires a password to read and edit the drive. All tasks are done in Disk Utility. Plug in the external drive you wish to encrypt: Make sure all previous data on the drive has been …
This tutorial will walk an individual through the process of installing the necessary services and then configuring a Windows Server 2012 system as an iSCSI target. To install the necessary roles, go to Server Manager, and select Add Roles and Featu…

914 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

21 Experts available now in Live!

Get 1:1 Help Now