Archive for February, 2008

VirtualCenter 2.5 Passthrough Authentication

February 28, 2008

At last! VMware have finally added passthrough auth support in VC 2.5, although it is currently classed as experimental. This is something I have been waiting / asking about for quite some time. And even better, it’s on by default! To use it, simply add -passthroughAuth -s vchostname to the end of the shortcut used to launch the VI 2.5 client.

By default it uses the Negotiate SSPI provider, however since they have fully implemented the interface you can change that behaviour to use Kerberos by adding the following within the <vpxd> node in the vpxd.cfg file on the VC server:


VMworld Europe 2008 has almost been worth it for this little gem alone, as you won’t find it on any slide deck – the information came straight from the presenters mouth in conjunction with a quick consultation of the VC source code (by him, not me 🙂 in order to determine the correct entry for vpxd.cfg. I will now work out how to use this with custom written SDK apps, although I have a suspicion it will be a fairly simple matter of passing the same arguments as part of the connect sequence. Will be sure to post when I figure it out!


Datastore Design Considerations

February 21, 2008

Been a bit of a slow month, although hopefully it’ll be a strong finish as I’ll be at VMworld Europe next week :-). .

The inspiration for this post is the flurry of marketing BS going on in the storage space currently – mostly due to VDI. From most cases I have seen / heard about, the storage cost ranges from between 1/4 and 1/2 of the total cost of a virtual desktop. And it’s more often than not a recurring charge.

So any business unit worth their salt will soon question just why they are paying this recurring charge that over the course of 6 months probably comes close to the once of cost they used to pay for a physical desktop that they kept for 3 years. Which inevitably makes it’s way back to you to re evaluate your current storage design, and inevitably ends up with storage vendor marketing hyperbole flooding the internet.

‘Thin Provisioning’ and ‘de-duplication / single instancing’ are the buzzwords of the day, but what implications do these various technologies have on your datastore design? The question needs more careful consideration than your CIO who has just watched this or this may care for.

Lets take the first video from incumbent FC champion, EMC. Aside from the fact that it’s all whiteboard, the presenter either doesn’t know the details of what he is talking about, very craftily steps around an important technical detail, or knows something that none of the storage engineers I work with know. Since the ppl I work with are a pretty damn smart bunch, I suspect it’s not the latter.

The important technical detail to note is that he doesn’t at any stage actually say he is referring to a VMFS LUN. Why is that important? Because of course, SAN based snapshots are LUN based. So when he takes a ‘master’ LUN, full copies it 4 times for better performance, and the proceeds to snap off 1000 VM’s from those 4 LUNs attached to the one ESX cluster… wait a minute, what was the LUN limit of an ESX host again?

Which leads to the inevitable conclusion that either he must be using an NFS datastore or VMware have finally rolled over to their parent company and EMC can now understand VMFS like no other storage vendor can. Queue the second video from the kings of NAS, NetApp.

Sure the video is a little far fetched (there is obviously no way you could actually run all those VM’s using no more than a 10GB of disk), but it illustrates the power of using NFS as a datastore – file based clones are possible, and if you’re gonna do NFS datastores then you could certainly do a lot worse than use NetApp. And before you go throwing VMware NFS vs iSCSI vs FC performance papers at me, know that NONE of their papers are based on NFS presented via a NetApp box.

The flipside to NFS via a NetApp however, is that thin provisioning goes out the Window because NetApp’s WAFL filesystem touches every block of the LUN it’s presented when it gets it (hey, there’s a reason why WAFL stands for ‘Write Anywhere File Layout’). VMFS doesn’t however, thus allowing for thin provisioned LUNs to work as expected although you may need to create .vmdk’s as thin too, which is not without caveats. I say may because 3PAR can actually handle the default zero’ed thick .vmdk format so if you’re using them you don’t need to change anything on the VMware side.

Which brings us to de-duplication / single instancing. This can’t be handled by the underlying storage array without some kind of intermediary thing… like another filesystem or OS… to scan for duplicate blocks and then manage what de-duped blocks belong to what higher up the chain, and then manage what to do if something higher up needs to write to a previously de-duped block etc etc. The whole point of disk subsystems in enterprise storage arrays is to do precisely none of that – it should be done at a higher level, ideally the native filesystem level. VMFS can’t do this (yet), but Vmware’s SVI will go some way to removing the need for de-dup in the first place. NetApp’s sis-clone feature has the same effect, will be interesting to see a performance comparison of the 2 when they go GA.

Funny thing is, no one seems to be talking much about the performance implications of stacking all these clones and snaps on top of each other. When 250 VM’s do something similutaneously that requires the IO to make it all the way down to the physical device (virus scan, anyone?), hows it gonna act? Better hope you got a ton of cache and nothing else is using it.

Finally, NFS may lead to an easier migration path because any worthwhile NAS box can present NFS and CIFS. So if you have a Citrix XenServer or *cough* Microsoft Hyper-V *cough* *cough* migration on the cards in the future and by that time all the vendors virtual hard disk formats interoperate, then you’ll save yourself a lot of pain on the storage side.

So what to do, what to do… as always, it depends on your environment. But I think more than ever, the old paradigm of ‘FC is king’ needs serious reconsideration, and VMware need to spend some time on VMFS rather than developing half arsed patching solutions (ouch – more on Update Manager during or after VMworld!).

Thanks Mike :-)

February 11, 2008

Thanks Mike for the nice linkup from RTFM-ed (as if I even needed to link that :-).

I’ve got my head down currently working on a little state management app that I hope to work into the PXE boot stuff, I’ll have to knuckle down even more now!

I know it’s kind of old now, but any Windows ppl interested in automating VI3 operations should check out the VI PowerShell toolkit. PowerShell provides a really nice abstraction layer between a GUI and the underlying infrastructure, it’s no wonder Microsoft are laying all their new management consoles on top of it. We can only hope VMware follow a similar track… it would be great to have PowerShell cmdlets for the new remote CLI for example. Having little ‘export as powershell’ button at the end of the VirtualCenter GUI wizards would be a nice touch too!

VM boot screen timeout

February 6, 2008

I’m always being foiled by the boot screen of a VM, even with a VI 2.5 client pointing directly at an ESX 3.5 host, the BIOS splash screen goes by way too fast for me to change the boot order.

Adding the following to the vmx file of the box sorts it out though

bios.bootDelay = “boot delay in milliseconds”

Might consider setting this to 5000 as a standard!

UPDATE As pointed out by reader Morgan, this is now configurable via the VM options in the VI client GUI. Thanks Morgan!