Running VNX on snapshot

Hi all,
I know running VM on a snapshot is not good in terms of performance and disk space. I have seen a client who runs a VM with a snapshot for a long time (two months so far).  The reason they keep the snapshot because the application breaks when the backup runs every day so they decided to keep the snapshot. I can not find any documental evidence to giving them that if you run a  VM with snapshot more 74 hours then chances the will break. As far as my client concern It is running ok and they want to keep it as it is.  Will they get a nasty surprise one day keeping the snapshot?
What would happen if you run the VM with a snapshot?
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sara2000Asked:
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Is this a VMware Snapshot or SAN Snapshot ?

Performance is degraded running on a snapshot. (difference disk!)

Snapshots can only be the same size as the parent virtual disk.

There is a maximum number of snapshots per disk.

The storage (datastore) could run out of disk space.

Snapshots can very easily be corrupted. and if they run a snapshot for two months, in the event the snapshot becomes corrupted, they will lose 2 months worth of data, because the snapshot will revert to parent disk, and may have corruption.

If they decide they want to committ the snapshot, e.g. remove it correctly, it could take many days, weeks or months to complete, causing many weeks, months of downtime!

It depends on how active a VM is, how quickly the snapshot will grow.

If they are happy with the performance, and don't want to apply best practice!!!

They really need to identify the fault, rather than run on a snapshot.

To be honest, we try and encourage ALL our clients to check for snapshots daily after backups, to ensure there are no snapshot issues, and reduce the risk of Snapshot Hell.

HOW TO: VMware Snapshots :- Be Patient

Some time in the future, you will be able to advise your client "I told you so...." Until then I wish them good luck with this bad practice!
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sara2000Author Commented:
Thanks, Andrew, I have a question about
Snapshots can only be the same size as the parent virtual disk.[/b]
Does this mean that snapshot disk will grow until it reaches the size of parent virtual disk over the period and then  VM will stop?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Does this mean that snapshot disk will grow until it reaches the size of parent virtual disk over the period and then  VM will stop?

Yes VM will fail. If it does not fail before, because of too many snapshots, not enough storage, or gets corrupted - pick one of the above!

Snapshots are designed for use as a temporary solution, really to allow backups to operate (poorly!), and Snapshots have been VMware's VMs Achilles heel, since the damn things were invented!

Experts Exchange gets a snapshot question issue weekly.... and our service desk daily, they are the most mis-understood VMware function, the next is VMware Converter P2V, followed by vCPUs!
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sara2000Author Commented:
Thanks, Andrew, it is a good article, will forward the link to the Tech to read it.
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
They are playing Snapshot Russian Roulette!

Ticking Time Bomb, and it's only going to end one way - BAD
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sara2000Author Commented:
I forwarded your link. It is a great article.
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
thanks for your kind words.
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robocatCommented:
I concur with Andrew: from our experience, the longer you keep a snapshot, the bigger the chance it will go wrong.

How does your client perform backups and why does the application fail if they do the backup? Does this mean they take no backups at all? One thing is for sure: snapshots are not backups.
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Ajay ChananaMCSE-2003/08|RHCSA| VCP5/6 |vExpert2018Commented:
The main purpose of snapshot is to keep the OS safe from any unexpected damage.

Having said that you require snapshot , when you upgrading or patching your OS and you don't know what would be the result after that.

If the VM works find and application running as expected, delete the snapshot. If the VM is not running find revert it.
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