There seems to be a mis-conception that the VMware HA (High Availability) component gives application level available near-zero downtime. In a recent document review I found a reference touting it to be better than Microsoft Cluster Services and could replace the MSCS offering. Err, let’s have a look at the differences.

Why VMware HA isn't MSCS

Microsoft Cluster Services IS application aware. It’s aimed at the high end / high service availability applications such as MS Exchange or MS SQL.

If you can’t suffer application downtime choose the MSCS and stick it in VMware although I would highly recommend reading the VMware and MSCS documentation first – there are caveats.

VMware KB Article 1004617 aligns the support statements of VMware ESX versions to Microsoft Cluster Services

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1004617

(steps down off soap box)

The default action with VMware ESX(i) when applying a snapshot is to create the relevant snapshot files in the working directory of the virtual machine. In an environment using VMFS datastores with a single block size across all LUNs this works fine however; where datastores exist for specific applications requiring large VMDK files an issue can occur.

Scenario

datastore-1 formatted with 1mb block size for VMDKs < 256gb hosting a virtual machine ‘C:’ drive, circa 40gb.

datastore-2 formatted with 2mb block size for VMDKs > 256gb & < 512gb hosting a virtual machine ‘E:’ drive, circa 350gb.

VMware VCB or an administrator (in this case Mr Snappy) issues a snapshot.

Mr Snappy with the VMware Admin handbook

The snapshot will fail to apply and return an error to the VI client console or to VCB.

The resolution

A new datastore will need to be created and formatted with a block size equal to the datastore where the large VMDK file resides. Power down the guest operating system / virtual machine then add an additional line to the virtual machine VMX file, this being:

workingDir=”/vmfs/datastore-name/”

Finally, the virtual machine will require re-registering. Either remove it from the inventory then browse the datastore to add it back in or use the vmware-cmd -s at the command line. Whichever way you feel more comfortable with. If you’re not using the vMA but need the command line for ESXi see this article to get an SSH console.

Further reading can be found within VMware KB article 1002929.

It’s an age old ‘virtual’ discussion and one I’m working with at the moment. A raft of virtual machines all *needing* 4xCPUs but when challenged no qualification can be evidenced.

Stuck on the motorway this morning this analogy leapt to mind.

Consider, you’ve organised a road trip holiday, more than likely you’d plan like this.

Yes, good idea

1. Full tank of fuel
2. Pack a kit bag with your clothes and essentials
3. Pack enough food to get you started and keep you running for a predictable while
4. Subsequent stops during the tour would be for re-fuelling to keep the balance going
5. A happy medium would be found

That would seem a sensible approach and would be similar to adjusting the resources within a Virtualised Infrastructure to meet the demands of a virtual machine to be shaped around business needs.

No, bad idea

A somewhat daft approach would be:

1. Divide total mileage by the estimated range in the tank and realise you need 12 full tanks
2. Accommodate the 12 tanks by stripping out the seats out and filling the vehicle with jerry cans
3. Calculate roughly how much food you’d need for the few weeks journey
4. Pack boxes and boxes of food (some perishable)
5. Clothes, well they may well fit into the glove box…
6. Additional passengers? Hmm, squeeze in and sit on the lap of the driver or jerry cans

Top heavy virtual machines?

Throwing everything in one go really doesn’t work for a holiday so why apply the “I need all resources immediately” for a virtual machine requirement.

I’ll be using this analogy again… and again… and again…