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dgriffnz
Contributor
Contributor

Snapshots, copying VMs etc

Hi,

I was just wondering if someone could provide a basic rundown of the role of snapshots. At the moment if I require a new 2003 server I copy the vmdk's of my basic install image, rename them and then start up a new server with a new SID, IP addy and name. A backup of all my vmdk's are simply stored on a ext usb hdd.

I'm just trying to come to grips with some of the basics of what's the best practice etc when using VMs - I've not been shown other ways of looking after my VMs.

TIA

DG

ps...i'm a bit of a ESX noob if you hadn't guessed...

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Dave_Mishchenko
Immortal
Immortal

There's a good article on snapshots at the first link and some further reading with the second. Basically a snapshot allows you to freeze disk writes to the original VMDK file. Changes made to the "disk" are instead written to a snapshot file. At some point you can either choose to commit the snapshot (at which time all the disk changes are written to the VMDK file, or to discard the changes, it which the VM goes back to the way it was before the snapshot was taken.

Some uses:

- online backup - you take a snapshot of the VM while it is on. You can then backup the VMDK and have it be in a consistent state, because all disk changes are being written to the snapshot file. After the backup is done, the snapshot is commited and all the changes made during the backup are written to the VMDK file.

- testing upgrades - patches - etc - you take a snapshot of the VM and then install your patches, config changes, etc. If you don't like the way it goes, you discard the snapshot and things are back to the way they were before you started the changes.

http://www.petri.co.il/virtual_vmware_snapshot.htm

http://www.vmware-land.com/Vmware_Links.html#SNapshots

PS - if you have VirtualCenter, you can clone VMs with it.

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digitalex
Contributor
Contributor

Dave,

Are there any restrictions to the type of server that should not be snapshotted? We use Windows 2003 and Windows 2000 Servers including AD, DHCP, DNS, File Share, and SQL Databases.

My current setup for info: Virtual Center 2.1 ESX 3.5 up1 on 3x HP DL460c G1 16gb EVA4100_1 20 Windows 2003 Ent VM's
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ChrisDearden
Expert
Expert

AD / DHCP /DNS / File and print Are fine.

SQL is a little bit different as the backup you make with the snapshot is not nessesarily "crash consistent" as transactions still in RAM would not be on the disk. If you want to use the snapshot as a precursor to a backup , you should really stop the SQL service ( this isn't required with VCB , which can use the Volume Shadow writer to take crash consistent backups )

You can chain snapshots , but be aware that if you go beyond about 4 , it'll hammer your ESX host into the ground.

If this post has been useful , please consider awarding points. @chrisdearden http://jfvi.co.uk http://vsoup.net
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digitalex
Contributor
Contributor

Yes I mainly want to use snapshotting with the capabilty of VCB to tape. So I should always use VSS to get crash consistant backups?

My current setup for info: Virtual Center 2.1 ESX 3.5 up1 on 3x HP DL460c G1 16gb EVA4100_1 20 Windows 2003 Ent VM's
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ChrisDearden
Expert
Expert

VSS snapshots should make Exchange / SQL backups crash consistent. its pretty easy to enable.

Ducan Epping sums it up nicely here:

http://www.yellow-bricks.com/2008/07/26/vss-snapshots/

If this post has been useful , please consider awarding points. @chrisdearden http://jfvi.co.uk http://vsoup.net
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