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vmware common mistakes and horror stories

if you do any sort of vmware healthchecks/audits for external organisations or even those you manage, are there any common virtualisation/vmware configuration or management mistakes organisations make, and any common horror stories on those mistakes that you could share (obviously keep the company name out).
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pma111
Asked:
pma111
3 Solutions
 
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
1. Lack of IP Address management, and hence IP Address conflicts, and therefore the host server goes down.

2. Lack of Storage Management - datastores fill up and no VMs can be started.

3. Not checking VMs for Snapshots, and hence VMs fail.

4. Not checking that Backups run, or Test Restores.

5. Tripping over power cables in the Datacentre and pulling out power cables to Hosts or SAN.

6. Letting Staff e.g. cleaners into datacentres, which is a restricted area, and using a vacuum cleaner, and blowing the phase fuse, resulting in datacentre failure.

7. Not checking that DR Site circuits are complete for failover.

8. Not ensuring that fire detectors are regularly serviced, and hence a fire gets out of hand in the datacentre causing, Datacentre out of action.

9. Completing upgrades to Finance Baking Computers, and not testing the upgrade causing 3 days outage, and customers not able to access funds.

10. Completing upgrade to authentication system, and causing ATM/Debit Cards not to function.

11. Now generator of UPS available, and when the power lines were cut, by contractor, no customers able to make cellphone  calls, because servers were down, no DR site.
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SagiEDocCommented:
1. Not tagging ALL VLAN's or tagging VLAN's that were not present thus causing VM's to lose connection to network after a migration.
2. Not specifying all iSCSI targets causing VM's to lose connection to storage.
3. VMware tools not kept up to date resulting in VM's performing badly.
4. Not paying attention when installing ESXi, resulting in the ESXi installation overwriting VM datastore - client did this three times before realizing the mistake.
5. Storage backup batter failed resulting in the storage cache being disabled - Very bad VM performance as a result.
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jhyieslaCommented:
Improper use of snapshots.

I've found that a lot of people think that snaps are either a back up scheme or that you can take as many as they want and save them forever.  This is a sure way to get into trouble with VM performance and disk space usage.

In short, when you take a snap you are NOT making a copy of your running VM.. You are making your VMDK file (the file that is the VM) read-only and creating a delta file.  While the snap exists the delta file grows as it keeps track of all the changes that are happening to the VM since those changes can't be written into the VMDK file. When you are done with the snap you have two choices. One is to consolidate it into the VMDK file which in effect keeps everything that has been done on the VM since you took the snap. The delta file goes away and the VMDK file becomes R/W again. The other thing is if you created the snap before making some change and that change went wrong, you can revert to the original VMDK file which means that the delta file is deleted wihtOUT rolling the changes into the VMDK file, the VMDK file becomes R/W again and the VM goes back to it's state before you did the changes.

Unless you store your snaps elsewhere, you also need about as much free space on the drive as the delta file is big. In other words if you've let the delta file grow to 2 GB you will most likely need 2 GB of free space in order to consolidate it back into the VMDK file.
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pma111Author Commented:
Good pointers, thanks
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