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vmchr1s
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VMDKs + snapshots cause performance issues?

Can think VMDKs w/ snapshots cause performance issues by any chance?

I'm on vSphere 4.1 (esxi)

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RParker
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vmchr1s wrote:

Can think VMDKs w/ snapshots cause performance issues by any chance?

I'm on vSphere 4.1 (esxi)

Yes and No.

Let's say you have VM-1.  VM-1-snp (snapshot)

If you have a database running on a VM, and you create a snapshot, the data is READ from VM-1.vmdk, and WRITTEN to VM-1-snp.vmdk but databases need a LOT of IO, so going back and fourth could cause an issue.

Otherwise performance isn't an issue normally with snapshots.. space is the problem, and the time to commit the data is the biggest problem, because your SAN/drives will take a significant hit during snapshot delete / commit data.

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VMmatty
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Can you clarify what you're asking?  Are you asking if simply having a snapshot on a VM can cause a performance problem?

The biggest performance hit you'll likely experience is when you delete a snapshot.  The behavior of snapshot deletion has gotten better since ESX 4.x, but it still requires copying all of the blocks into the original VMDK which can cause a lot of disk I/O.  So beware of letting your snapshots grow too big since deleting them can take a while and affect performance.

Matt

http://www.thelowercasew.com

Matt | http://www.thelowercasew.com | @mattliebowitz
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RParker
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vmchr1s wrote:

Can think VMDKs w/ snapshots cause performance issues by any chance?

I'm on vSphere 4.1 (esxi)

Yes and No.

Let's say you have VM-1.  VM-1-snp (snapshot)

If you have a database running on a VM, and you create a snapshot, the data is READ from VM-1.vmdk, and WRITTEN to VM-1-snp.vmdk but databases need a LOT of IO, so going back and fourth could cause an issue.

Otherwise performance isn't an issue normally with snapshots.. space is the problem, and the time to commit the data is the biggest problem, because your SAN/drives will take a significant hit during snapshot delete / commit data.

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vmchr1s
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Any difference if it's thick or thin though?

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continuum
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> Can think VMDKs w/ snapshots cause performance issues by any chance?

yes - of course
the more snapshots you have and the larger they are the slower and the more fragile the VM becomes


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