Can I recover a VM if a snapshot has been performed prior to the VM being corrupted?

If a VM becomes corrupt and the OS will not start after patching it, can I recover the VM if I took a snapshot of it prior to patching the VM? How would I restore the snapshot? Will it restore to the state it was in prior to patching it? How much space does a snapshot generally use up? We are running vSphere 5.5.
joukiejoukAsked:
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Neil RussellTechnical Development LeadCommented:
Yes you can just revert to the current snapshot.  
As to size?  A snapshot takes up space as you make changes to disks AFTER the snapshot is taken.  if you take a snapshot and then write 1GB of new data to a disk, then your snapshot will grow by 1 GB. etc..
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Tom Jacob ChirayilSystems EngineerCommented:
If the VM is a domain controller, don't revert the snapshot. The USN number will go out of sequence and then you will have to demote and promote it back as the domain controller
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
If a VM becomes corrupt and the OS will not start after patching it, can I recover the VM if I took a snapshot of it prior to patching the VM?

Yes, this is what Snapshots were designed for we believe, although we do not use them, we ensure we have a full backup of the VM or Clone before we change anything in a VM.

How would I restore the snapshot? Will it restore to the state it was in prior to patching it? How much space does a snapshot generally use up? We are running vSphere 5.5.

Do do not restore, snapshots are not backups. You would  Right Click the VM, select, Snapshot Manager, and select Go To the Snapshot you took  before you updated the VM with patches. and then IMPORTANT, DELETE the snapshot.

The process of go to the snapshot, is a rollback in time, so when the VM starts, it will be reverted or as you call it restored.

You then need to remove/delete the snapshot, so it's not combined.

As for Size of Snapshots, it's not quite simply if you copy 1GB in, the size changes by 1GB.

Snapshots are deltas, e.g. changes....to the OS.

Roughly a snapshot can increase by 1GB per hour the machine is running, depending upon it's activity.

We would personally advise against using snapshots, as they are difficult to manage, take up additional disk space, which if becomes full, VM will stop, and disk can be corrupted, and also performance of a VM running on a snapshot is slow....

see my EE Article I wrote...

HOW TO: VMware Snapshots :- Be Patient
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joukiejoukAuthor Commented:
Some systems that I have created snapshots for last Thurs were having issues over the weekend. Come to find out, snapshots that were created were taking up disk space. I removed the snapshots from snapshot manager, which i believe fixed the issues with these servers. Is there anything more I need to do other than deleting the snapshot's I have created? Is it best practice to remove these snapshots after a day? Do these snapshots write to disk on the server, or on the SAN the server resides on?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Snapshots are a file, that take son space on the SAN, you must delete snapshots, through the integrated Snapshot Manager.

VMs running on snapshots, perform poorly, and are based deleted.
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