In a cutthroat industry where there is little to agree on, execs from top storage vendors had no problem finding common ground on an aspect of Microsoft’s System Center Virtual Machine Manager (SCVMM).
It turns out that when an administrator connects an ISO (slang for a CD or DVD image file) to a virtual machine, SCVMM deploys a copy of the file to the virtual machine’s directory. Templates made from such a virtual machine also retain their own independent copy of the image file. SCVMM even extends the favor to managed VMware environments by making a copy via SFTP to an ESX host.
Unknowing administrators accustomed to the single shared image approach employed by VMware VirtualCenter may be in for a surprise when gigabytes of expensive SAN storage suddenly start to disappear.
In a recent (made-up) summit on ISO image file deployment best practices, top industry thinkers weighed in:
“If there is one thing we can agree on,” said one source insisting on anonymity, “we really prefer SCVMM’s handling of ISO images over VirtualCenter. We also obviously prefer one VM per LUN and substantial overallocation for snapshots and future growth.”
“Absolutely,” agreed another. “We wholeheartedly embrace the concept of copying the two to four gigabyte DVD images from one central repository to the SAN whenever possible. And please, do not go back and remove the image files after using. They may be needed again someday.”
One storage analyst wrote in a whitepaper curiously sponsored by three top storage vendors:
While VMware’s VirtualCenter may allow administrators to connect multiple virtual machines to a single, shared instance of an image on the SAN or on an inexpensive NFS share, we do not encourage that design. We have found that practice to seriously impact storage shipments and next quarter’s numbers the overall satisfaction of our customer virtualization SAN deployments.
It is not at all clear why VMware chose to take this minimalist approach. After all, the improved manageability of replicating identical ISO images throughout hundreds of virtual machines and templates is much more analogous to non-virtualized storage and physical CD-ROMs. Isn’t the leading virtualization company concerned about providing their customers an equivalent experience?
Are you pro- or anti-ISO proliferation? Did you have a choice?
Folks, this article is satire. Lighten up.
Did they also recommend storing the original ISO files on SSD? I’ve heard from those same vendors that it’s required to get optimal performance.
😉
😀
great way to start this morning, with a laugh. thanks!
This post was brilliant. Great job conveying the topic with humor. Now all we need is Windows 7 to be distributed on Blu-Ray disks, and our budgets will go poof.
I, for one, welcome our new ISO file overlords.
All my .ISOs and seasons 1-4 of The Brady Bunch goes on Tier 1 storage for best performance.
Gentlemen, thank you for the feedback. I was not sure how well humor and technology were going to mix, but it looks like it worked.
I am currently testing the RTM version of SCVMM in my lab and I just had to test the ISO issue…
I found that you have the option of ‘Sharing’ the ISO from the SCVMM library instead of copying it local to the host that is running the VM. This is not the default setting and you also have to edit the permissions on the SCVMM library share and NTFS folder permissions to allow the sharing.
However the ESX servers will not be able to mount an ISO from the SCVMM library via SMB share, so it will be copied.
Although there is a workaround to not copy the ISO files, the connection from the Library to the Host is via network share instead of SAN, because unlike Vmware where you can create a VMFS volume for ISO files and share it amongst all your hosts for installing from media, Microsoft does not have a clustered filesystem that would allow all of the hosts access to a volume for this purpose. (This is also one of the reasons for the lack of Live Migration and the need for one VM per LUN for Quick Migration)
Just another example of the lack of maturity currently in the MS product.
Shawn, did that sharing actually work for a Hyper-V host? This is what the online help says:
Share image file instead of copying it. Selecting this option saves space on a virtual machine that is created by using this hardware profile. This option is only available on Virtual Server.
I assume it works.
I created an ISO directory in the SCVMM library share, and copied an .iso.
It was discovered and was then available when I edited the CD properties of a VM.
The first time I tried to mount it, I received an error because the VM ‘XPTEST’ did not have permissions to the file. I then edited the SCVMM Library share permissions to read only Everyone and changed the NTFS permissions on the directory to the same.
The CD then mounted properly.
Hmm. I tried what you suggested with no improvement. When creating a new VM, the UI specifically explains that the host does not support sharing images and will not even proceed. Connecting a shared image to an existing VM causes all kinds of errors. Considering the online help also states this is not supported on Hyper-V, my original thesis stands.
Thanks for the input, though.
I have only briefly looked at your site here after someone sent me this hilarious posting, but so far I have noticed no one mentioning Xen. This site seems to be a no-holds bared site, (even though Eric works for VMware). Does anyone have comments on how Xen handles their ISO library?
Hi Bruce,
Not sure what flavor of Xen (Open-source, Citrix, SunXvm, RedHat, OracleVM, Virtual Iron, etc) you’re referring to but I have some experience with Citrix’s XenServer and their management tool, XenCenter, so can provide some insight here. XenServer can only use a standard Windows CIFS share or an NFS share to store ISO images. Local storage of isos are not supported. No agents need to be deployed like in SCVMM Library Servers. Just create a storage repository for the CIFS or NFS ISO share and your VMs can access them. It also doesn’t copy the entire ISO over to the VM like with SCVMM.
By the way, I’ve been using XenServer since version 3.5 and Citrix has just finally implemented full iso support for VMs. In previous releases they didnt support using ISOs to install some linux VMs, only Windows. As a result your forced to create a Linux install server to stream the install. It was a major pain! Seems that they finally got the ISO support down in version 5 (about time!). So if your looking at any other Xen hypervisor products, it may not have full support for even installing VMs with ISOs.
Let me know if you have any additional questions on XenServer and I’d be happy to share.
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You have found a bug.
More info:
http://joeelway.spaces.live.com/blog/cns!2095EAC3772C41DB!1757.entry
Softwares always have bugs. See some resolved issues here
http://www.vmware.com/support/vi3/doc/vi3_esx35u3_rel_notes.html#resolvedissues
The bigger part of the problem is not to communicate this in any formal way (e.g. in support.microsoft.com site)
Tamas: thanks for your comment, but this is not really a bug. A bug in the design, perhaps. Consider that the online help states that this is not supported for Hyper-V and the SCVMM console throws up warnings when attempting to provision a new VM with sharing enabled. If it was just a bug, the docs would be silent on this and the user interface would let you proceed.
You are right about all software having bugs. Believe me — I have personally filed many, many bugs on ESX and VC.
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I think this is great! buy more disks for iso storage! excellent!
I posted the workaround if it matters http://www.thegenerationv.com/2009/08/sharing-iso-image-using-hyper-v-and.html
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