Why snapshots are not recommended by Microsoft in a production environment?

I am wondering why snapshots are not recommended in a production environment by Microsoft in Hyper-V?
Also, I am wondering if VMWare is the same (not recommending snapshots in production)?

Thanks
J

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Y YconsultantAsked:
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Azeem PatelConnect With a Mentor System AdministartorCommented:
The below article will help you in many ways in considering or say when to use Snapshot.
http://technet.microsoft.com/en-us/library/dd560637%28WS.10%29.aspx

I suggest at least read twice the complete article.
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Lee W, MVPTechnology and Business Process AdvisorCommented:
Where did you hear this?  Please post the link as I believe you are mis-reading/mis-understanding.

You should not use snapshots on a DC because it can seriously corrupt AD if you restore one.  Other functions may also be subject to serious problems depending on what they are.
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geowrianCommented:
I"m familiar with the VMWare side of things, but can't speak on the Hyper-V rational. For VMWare, snapshots are fine for a production environment for many purposes. However, they are often used for the wrong purposes as well. In general:

When to use snapshots on a production system:
1) Prior to an application install/upgrade. This provides a fallback in the event the install/upgrade go catastrophically wrong. The snapshots should be committed once complete and the system is verified to be functioning normally.
2) Some full-system backup software use snapshots and then backup the virtual configuration and disk files. This creates an exact point in time copy of the running system and is OS-independent. Afterward, they commit the snapshot.


When not to use snapshots on a production system:
1) As an alternative to backups.
2) For almost any long-term purpose on a production system. The host has to keep track of where to read each section of data across all the snapshots.
3) During periods of high CPU, memory,network, or disk utilization. Snapshot creation and committal can use a lot of resources, especially network and disk IO. This can not only cause poor VM or general network performance, but is also more prone to errors or bugs. I remember an issue with Double Take causing a powered off replica to randomly lock some files on disk during high disk IO, which then put the entire production VM in an invalid power state.

I hope this sheds some light.
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geowrianCommented:
To backup what leew noted:

Snapshots obviously only affect the disks you have in the snapshot. If the system or application refers to other resources, it's a fishy deal. For instance, restoring a snapshot on a domain controller will cause all types of issues as other DCs, or even the workstations, are trying to reference data that the DC no longer has. And it can cause an Exchange server to become out of sync with the other Exchange servers or even AD in general. If you have a web application with a web front end and a SQL backend, you may need to snapshot both at the same time, and even that can get fishy depending on the application, and you should be prepared to restore from a backup in the worst case.
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geowrianCommented:
I read the URL you referenced, and have some responses/clarification below:

1) Performance: Noted in my original response
2) Disk space: Implied in my original response. With a snapshot, any changed or even deleted data actually adds to the size of the differential file (snapshot).
3) Downtime: This applies to Hyper-V, but not VMWare. VMWare deletes the snapshot files immediately upon committal.
4) Clustering: Similar to the notes by leew and my second response.
5) Physical disks: This isn't really a drawback to snapshots, but more of a limitation on using them. Snapshots have a number of requirements and restrictions. For example, you cannot grow a disk (in VMWare) if it has any snapshots on it. You also cannot snapshot an RDM.
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Lee W, MVPTechnology and Business Process AdvisorCommented:
I'll revise my statement - IF you are familiar with the issues, you CAN use snapshots but many people not familiar with those considerations as outlined in the blog post you can know when it's appropriate and when it's not.
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Andrew Hancock (VMware vExpert / EE MVE^2)Connect With a Mentor VMware and Virtualization ConsultantCommented:
As long as you have the disk space, don't use them for backup purposes, and don't let them get out of control, by having nested with nested snapshots and use them as intended, and don't use a snapshot for extended periods of time, or forget about it, because thje merge process will take many hours to complete. This is what people forget, and we have them all the time here on EE, with Snapshot issues because of this.
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coolsport00Connect With a Mentor Commented:
Speaking from VMware's standpoint, it is true that the use of snapshots should be used sparingly.
I've grown away from MS's solutions, but assume their use in that environment, at least mostly, will hold true as well.

Here is VMware's KB on 'Understanding Snapshots' better:
http://kb.vmware.com/kb/1015180

and 'Snapshot Best Practices':
http://kb.vmware.com/kb/1025279

Regards,
~coolsport00
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Luciano PatrãoICT Senior Infraestructure  Engineer  Commented:
Hi

I think that what you mean is that Snapshots is never recommend as a backup solution.

This is for Hyper-V or VMware or other Visualized System.

Other then this, I see no problem using this, and this is the first time I hear this.

Jail
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Diesel79Connect With a Mentor Commented:
Just my 2 cents but from experience snapshots complicate matters when using VSS writers for offsite backup purposes.

Here is my senario (if anyone has a better answer to this let me know!)

I use a homebrew set of powershell scripts to backup all of my VMs to offsite storage. This works extremely well for me and I have a fully viable backup each and everytime that I can bring online on a secondary SAN/VM Host setup.

At first I did not realize that the consultant we hired to upgrade our exchange box had used snapshots during his process, they had since been deleted and werent readily appearent. What this caused is the original .VHD files were then split with secondary avhd files containing snapshots.

It ended up being a very time consuming process to play the additional snapshots back into the primary vhds.

Bottom line is I dont like the vhd file seperation and would rather keep everything self contained. My suggestion is if you have a SAN type device leave your snapshots up to it and out of hyper-v, if you do not have a device of that sort I would probably use a dedicated hard disk (even if external) in combo with Windows Server Backup or write your own powershell scripts for the VSS writers that are included in 08 R2.

Deisel79

Deisel79
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Y YconsultantAuthor Commented:
Hanccocka:
You mentioned "... because the merge process will take many hours to complete"

Did you mean that a snapshot can be merged into its "parent"? If so, can you point me the URL about this for more details if possible?

Thanks
Jack
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geowrianCommented:
When you "commit" a snapshot, it merges the snapshot delta and it's parent (either another snapshot or the flat file), then deletes the snapshot.
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coolsport00Commented:
"techcity", the KB I posted about "understanding snapshots" explains this idea/concept.

~coolsport00
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Y YconsultantAuthor Commented:
geowrian & coolsport00:

"When you "commit" a snapshot, it merges the snapshot delta and it's parent (either another snapshot or the flat file), then deletes the snapshot."

- Does above statement remain true for Hyper-V? I am not using VMWare.

Thanks
jack


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coolsport00Commented:
Ah, ok; I can't comment on Hyper-V...my apologies.

~coolsport00
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geowrianConnect With a Mentor Commented:
I can't verify if Hyper-V does that as well. I did read that Hyper-V keeps the snapshots around until you power off or reboot the VM, which indicates it probably doesn't merge them immediately.
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