VMware Cloud Community
logiboy123
Expert
Expert
Jump to solution

2TB LUN's and Extents Clarification

I have a need to assign a several VM's in my clients environment with 2TB vmdk files, but I also want to be able to take snapshots of those servers.

Because of this I was hoping to the community could clarrify a few points for me by correcting any of my points/assumptions;

1) VMFS datastores can be a maximum 64TB in size.

2) VMDK's can be a maximum of 2TB in size.

3) Expanding a VMFS datastore and LUN requires that there be empty/free space at the end of the disk.

4) Creating a VMFS datastore greater then 2TB requires creating and presenting to ESX(i) several LUN's and then binding them together using Extents.

5) Expanding a LUN/VMFS beyond 2048GB is bad news and can cause data corruption.

So in my situation it seems to me that I need to create a LUN of 2TB and a second LUN of say 300GB, then bind them together using an Extent to create a VMFS datastore that spans the two LUN's and has a total of 2.3TB of space. Then I can create my 2TB VMDK and still be able to take snapshots.

Is there any other or better way to achieve my result?

Is there any concerns with using Extents, what is the trade off?

Any other comments would be welcome.

Cheers,

Paul

Reply
0 Kudos
1 Solution

Accepted Solutions
a_p_
Leadership
Leadership
Jump to solution

What is your process to seperate out the virtual disk configuration file from the virtual disk storage files?

Nothing special. When you create the VM select the first datastore. Then, when you create the virtual disk in the wizard, just select the second datastore

What is the penalty or drawback for using extents?

They are just not necessary anymore. Extents had to be used before ESX(i) 4.0 to resize a datastore. With ESX(i) 4.0 it is now possible to resize/grow the datastore on the fly after resizing the underlying LUN without the need of extents. With Extents you loose this option. Basically an extended datastore is like a RAID 0.

You may also read http://www.yellow-bricks.com/2009/03/26/resizing-your-vmfs-the-right-way-exploring-the-next-version-...

André

View solution in original post

Reply
0 Kudos
5 Replies
a_p_
Leadership
Leadership
Jump to solution

IMO using extents does not make any sense and should be avoided.

In your case, I would create two separate datastores. The first datastore with an 8 MB block size, in which you place the configuration file for the VM, large enough to hold the snapshot size you expect. Create the VM's virtual disk on the second datastore with an 8 MB block size. This way you can use the full size of the second datastore for the virtual disk, since the snapshots are created in the VM's base folder on the first datastore.

You will find the max. virtual disk size you can use, if you still want to be able to create snapshots at http://kb.vmware.com/kb/1012384

In your case the max. size for the second datastore is 2TB minus 512 Bytes and the max. size for the virtual disk is 2,032 GB.

André

logiboy123
Expert
Expert
Jump to solution

Thank you for your answer.

What is your process to seperate out the virtual disk configuration file from the virtual disk storage files?

What is the penalty or drawback for using extents?

Reply
0 Kudos
logiboy123
Expert
Expert
Jump to solution

I just had a thought.

So I could create a large VMFS datastore that only holds several VM disk configuration files. When I invoke a snapshot they would be produced in this drive instead of the datastore that holds the VMDK.

How does this affect storage VMotion; I know I can have the configuration file storage in a separate drive from the main disk files, but it's just something we need to be aware of when doing a storage VMotion, i.e. make sure to click advanced and select the storage area implicitly for each component?

Reply
0 Kudos
a_p_
Leadership
Leadership
Jump to solution

What is your process to seperate out the virtual disk configuration file from the virtual disk storage files?

Nothing special. When you create the VM select the first datastore. Then, when you create the virtual disk in the wizard, just select the second datastore

What is the penalty or drawback for using extents?

They are just not necessary anymore. Extents had to be used before ESX(i) 4.0 to resize a datastore. With ESX(i) 4.0 it is now possible to resize/grow the datastore on the fly after resizing the underlying LUN without the need of extents. With Extents you loose this option. Basically an extended datastore is like a RAID 0.

You may also read http://www.yellow-bricks.com/2009/03/26/resizing-your-vmfs-the-right-way-exploring-the-next-version-...

André

Reply
0 Kudos
hicksj
Virtuoso
Virtuoso
Jump to solution

Regarding extents, its really a matter of where do you actually want to be managing your storage environment?  I (and many others) believe you want to push as much of that off to the SAN, avoiding that level of management within ESX.

Of course, for some of us, the SAN may be old, inflexible, mainframe centric, etc and can't dynamically grow LUNs or do lots of other fancy stuff behind the scenes.  In those situations, you may not have much choice.  There's always dynamic disks to merge vmdks and create larger volumes within your Windows OS... I prefer that over extents in ESX, because the process is somewhat consistent whether the server is virtual or physical.

Regarding Storage VMotion, I believe what you stated is proper... use advanced to specify targets.

Cheers,

J

Reply
0 Kudos