Growing a LUN

[cef2lion]

We have an IBM DS4300 SAN presenting a RAID 5 LUN to a set of Dell 2950 ESX 3.5 servers. We would like to grow the LUN to increase its size. I wanted to see if that is possible with ESX and if so what steps do you take? Shutdown all guest OSs first. Do not want to damage the file structure or windows guest OSs. If not possible I guess I create another LUN with the left over space.

Craig

[weinstein5]

If you are asking to grow a LUN then grow the VMFS datastore that resides on that LUN - it is not possible - the best you can disk is the disk you were going to use is create a new LUN and create an extent for your original LUN - the best hough is just create a seperate VMFS datastore -

[Texiwill]

Hello,

As weinstein5 points out, the only option is to use an extent. It is recommended however that you avoid extents as they cause other issues, specifically when you try to get rid of them. If you have the space, it would be best to copy the VMs to a temporary location, delete the old LUN, and then make a new LUN of the correct size. Or deal with two distinct LUNs. More LUNs tend to be better than one giant LUN when it comes to SCSI Reservation conflicts.

Best regards,

Edward L. Haletky

VMware Communities User Moderator

====

Author of the book 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', Copyright 2008 Pearson Education. CIO Virtualization Blog: http://www.cio.com/blog/index/topic/168354, As well as the Virtualization Wiki at http://www.astroarch.com/wiki/index.php/Virtualization

[cef2lion]

Good information. Thank you. If I did create an additional LUN. Would it be best to break the RAID 5 down into less disks? If I create an additional LUN out of the space left on this original RAID 5 I'm going to be hitting the same disks anyway. Would it be better to create a series of RAID 1 LUNs with two disks and break things up over more disks?

Craig

[kjb007]

You will of course get less space with RAID1's then with the RAID 5 set. Remember that you can't grow a vmfs datastore, but you can add new space as an extent, or use the empty space as a secondary datastore. If you don't need the increased I/O that you will get with RAID1, then I'd stick with the RAID 5 and use the additional space for the vm's, since you're thinking about growing because you most likely ran out of space to begin with.

-KjB

[cef2lion]

Just in the first year with vmware and sorting out SAN storage needs. We are not out of space on the RAID 5 lun as yet but I see it coming. It was created as 400gig. I had a good bit left and at the time I didn't know if one could just extend using that space. Knowing I can't. I can just create another RAID 5 and present that. We are going to add a new SAN so by then I might have a better picture on how to layout the new SAN. We have 4 Dell 2950 ESX servers. Running a small windows forest for a campus at a University.

Craig

[cef2lion]

My RAID 5 array consists of 5 300gig drives. Since my LUN is 500gig. I have 600gig from the array uncommited. I can not grow the 500gig as I have found out here. I can create another LUN out of the uncommited 600gig but that will be to the same spindles.

Doing it over. I have other temp space I could move my VMs to and recreate the array. I assume I do not want to make an array over a terabyte. Is there an optimal RAID size I atick with? That way I can figure how many drives over 3 I should use per RAID 5 array. Once that fills I will create another RAID 5 array with more drives.

Craig

[kjb007 · Accepted solution]

The optimal size you'll find is around 15-20 vm's, or roughly around 300-500 GB. Any more, and you can run into reservations issues because of too many vm's. This is subjective based on the size of your vm's in general, so tailor to your needs.

-KjB

[cef2lion]

Thank you. Information I have been looking for.

Craig