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mark_a_k
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what happens to data when VM Snapshot is taking place

Hi, we are considering the use of snapshots of Virtual Machines. The Virtual Machines will be but into snapshot mode using Vmware utilites and it is my understanding that the VM will be unavailable for sometime while the snapshot takes place.. My questions is;

what will happen if some data is sent to the VM while the snapshot is taking place? Will the VM be reported as being unavailable or will the ESX server cache the data and commit it once the VM comes out of snapshot mode. The VM in mind will be Linux RH running mySQL. We want to make sure that attempts to write to the mySQL database during the snapshot will not cause the data to be lost.

Thanks for any information on this for both Windows and Linux VMs.

mark

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LarsLiljeroth
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Hi

We do alot of snapshot'ing in our invironment. And we have seen some problems on some servers. Mainly SQL servers.

If you do a snapshot with consistant memory you will normally se that the server is unavailable for 1-20 sec. In this period of

time you rely on the other end's capability to retransmit and capability to loose connection to the server and still continue communicting.

As far as i know the ESX servers does'nt hold any data in piriod of time where the VM is unavailable.

Also see this thread->> http://communities.vmware.com/message/752230#752230




Best regards

Lars Liljeroth

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// Lars Liljeroth -------------- *If you found this information useful, please consider awarding points for "Correct" or "Helpful". Thanks!!!

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LarsLiljeroth
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Hi

We do alot of snapshot'ing in our invironment. And we have seen some problems on some servers. Mainly SQL servers.

If you do a snapshot with consistant memory you will normally se that the server is unavailable for 1-20 sec. In this period of

time you rely on the other end's capability to retransmit and capability to loose connection to the server and still continue communicting.

As far as i know the ESX servers does'nt hold any data in piriod of time where the VM is unavailable.

Also see this thread->> http://communities.vmware.com/message/752230#752230




Best regards

Lars Liljeroth

-


If you found this information useful, please consider awarding points for "Correct" or "Helpful". Thanks!!!

// Lars Liljeroth -------------- *If you found this information useful, please consider awarding points for "Correct" or "Helpful". Thanks!!!
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larstr
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When you take a snapshot without including the VM memory, the VM will not be unavailable for any noticable time. Also, if VMware Tools is installed it will let the guest know that a snapshot is coming and VSS aware services will flush their io queues in order for the snapshot to be crash consistent.

Lars

larstr
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Since you're using a linux guest with a database running, the snapshots will not be crash consistent, and you should rather do a LVM snapshot from inside the guest os.

mark_a_k
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thanks for this information

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