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12 Replies Last post: Aug 19, 2008 7:34 AM by squirrelking
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Adding a hard disk greater than 256 GB

Aug 15, 2008 8:06 AM

Click to view brettcw23's profile Enthusiast brettcw23 19 posts since
Apr 15, 2008

We are creating a server for DR that stores all of our TS profiles.

The Prod box has a J:\ that is SAN atatched and is 700 GB.

So I wanted to create a 700 GB VMDK file on my DR box. But when I go to create the hard disk, it says that it exceeds the limit and won't go beyond 250 GB.

Does anyone have a work around for something like this?

Tags: hard, disk, vmdk, size
Reply Re: Adding a hard disk greater than 256 GB Aug 15, 2008 8:11 AM
Click to view Troy Clavell's profile Guru Troy Clavell 6,042 posts since
Oct 12, 2007

This is based on the block size of your LUNS. 1MB is the default and will only allow a 256GB max size. The only way that I know to do this is to reformat the LUN and present it will a bigger block size.

2MB = 512GB

4MB= 1024GB

8MB= 2048GB

We usually present our LUNS in our server cluster at 4MB block size.

Hope this helps

Reply Re: Adding a hard disk greater than 256 GB Aug 15, 2008 8:16 AM
Click to view wpatton's profile Expert wpatton 252 posts since
Sep 28, 2006
Please keep in mind that if you modify the block size of a LUN, it will destroy all data stored on that LUN. Before you make any changes, backup your data!

If you found this or other information useful, please consider awarding points for "Correct" or "Helpful".

Reply Re: Adding a hard disk greater than 256 GB Aug 15, 2008 8:17 AM
Click to view zelwyn's profile Lurker zelwyn 4 posts since
Apr 27, 2006
Make 3 250GB vmdk files and span them?

Zachary Elwyn
Engineer
Chase Card Services, Midrange-NT
301 North Walnut St., 16th Floor
Wilmington, DE, 19801
zachary.d.elwyn@chase.com
Reply Re: Adding a hard disk greater than 256 GB Aug 15, 2008 8:45 AM
in response to: zelwyn
Click to view brettcw23's profile Enthusiast brettcw23 19 posts since
Apr 15, 2008
That's what my proposal was but we just wanted to make sure that I wasn't missing anything within the VMware capabilities.
Reply Re: Adding a hard disk greater than 256 GB Aug 15, 2008 10:52 AM
in response to: zelwyn
Click to view aenagy's profile Enthusiast aenagy 92 posts since
Mar 27, 2005
VMFS volumes can not be spanned on the same LUN. Spanning should be avoided if possible.
Reply Re: Adding a hard disk greater than 256 GB Aug 18, 2008 1:21 AM
in response to: aenagy
Click to view BUGCHK's profile Master BUGCHK 953 posts since
Nov 7, 2005
I've tried it some time ago with ESX 3.0.x connected to a HP EVA storage array and it did work ---- 3 times, as the VI Client created an additional primary partition for the next VMFS extent.
Reply Re: Adding a hard disk greater than 256 GB Aug 18, 2008 7:43 AM
in response to: BUGCHK
Click to view aenagy's profile Enthusiast aenagy 92 posts since
Mar 27, 2005
Hmm, I seem to recall from my Install and Config course at VMware that this was not possible. Normally, I would not span volumes; we normally recreate the volume to avoid spanning.

Was the VIC connected directly to the host or was this done from VirtualCenter?
Reply Re: Adding a hard disk greater than 256 GB Aug 18, 2008 2:48 PM
Click to view squirrelking's profile Enthusiast squirrelking 77 posts since
Dec 9, 2004

It's generally against best practice from a VMware PS point of view to:

  • Create very large VMDK files that would need the larger than 256GB limit with a 1MB block size format.
  • Use "spanning" (by using extents)

Typically I always recommend using Virtual RDM's if you need anything larger than a 256GB virtual disk. You're performance will be alot better, especially in high I/O environments.

My .02,
squirrelking

Reply Re: Adding a hard disk greater than 256 GB Aug 19, 2008 1:06 AM
Click to view lfchin's profile Enthusiast lfchin 92 posts since
Oct 7, 2007

RDM will be the right choice on this case as it will not require too much extra work to be done

Rolando
http://itknowledgeexchange.blogspot.com/

Reply Re: Adding a hard disk greater than 256 GB Aug 19, 2008 4:51 AM
in response to: squirrelking
Click to view brettcw23's profile Enthusiast brettcw23 19 posts since
Apr 15, 2008

Pardon my ignorance, but what is RDM?

I actually created 3 .vmdk files 220 GB each. Then through the Windows OS, I used disk management to create one logical drive. The drive is going to be used for Terminal Server profiles. Does anyone see an issue with the way I set this up?

Reply Re: Adding a hard disk greater than 256 GB Aug 19, 2008 5:25 AM
in response to: brettcw23
Click to view lfchin's profile Enthusiast lfchin 92 posts since
Oct 7, 2007
RDM = Raw Device Mapping

in order to use this, you need to create the raid group from the SAN box you have and direct assign to the ESX host you need. Usually after this, we will add the storage from the virtual center and format it with VMFS. In this case, you don't need to format as VMFS as the Raid group will able to be attach to the VM you need through RDM from VM. when you try to add new harddisk from the VM, it will have the option to be choose as Raw Device mapping and you press next to it and choose for the available raid group which is unuse. the RDM will allow the VM direct write and read to the physical raid group from the SAN level

Rolando
http://itknowledgeexchange.blogspot.com/

Reply Re: Adding a hard disk greater than 256 GB Aug 19, 2008 7:34 AM
in response to: brettcw23
Click to view squirrelking's profile Enthusiast squirrelking 77 posts since
Dec 9, 2004

Rolondo is correct on his post on what an RDM is and how to add it..
More info can be found here: www.vmware.com/pdf/vi3_35/esx_3/r35u2/vi3_35_25_u2_admin_guide.pdf - Page 153. Note, you'll want to make sure to use the "Virtual" RDM type so that you're VM's can still be VMotion'ed and also used with VCB (if you use those features).

Also regarding Dynamic Disks (logical disks within Windows), take a look at this article for best practices:
http://support.microsoft.com/kb/816307
It lists some limitations of Dynamic disks and also areas that they are not supported. Typically in my dealings with dynamic disks and microsoft support, they will usually notice dynamic disks right away and will make you use a basic disk before they will further support you. It is well known within the Exchange communities and SQL communities to not use dynamic disks due to support issues.

Hope it helps,
squirrelking


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