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Qwantus
Contributor
Contributor

VCB questions - Tyring to get some understanding

We are planning to install and run VCB in the near future, the problem I currently have are basic understandings of the process. Let me give my impressions and have you explain where I'm wrong or right.

When doing incrementals... The proxy initiates a request (pre-script) for the VM to flush it's read/write buffers and snapshot. The next step mounts this snapshot somewhere that the proxy server can see. This snapshot isn't the same size of the VM, what is a good estimate for determining the size of a snapshot? For example, we have a file server running as a VM that has one HD 19GB (OS partition) and a Raw Device mapped drive for data of 1.23TB. On a normal backup night, is there a way to estimate the size of the snapshot for this server and does the snapshot it's self get copied to the proxy, or is the snapshot actually still in SAN storage and just pointers are mounted at the proxy?

Pretty much the same questions for Full Image backups... The above file server's image would be the total of both drives? And does that all get mounted in the proxy, or just pointers to SAN storage? Please remember that the second drive here is a raw device, How is it handled?

Thank you,

Qwantus

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Gerrit_Lehr
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Commander

Hi,

VCB works like this: It sets the VMs Disks into Snapshot mode, which means that the real vmdk becomes read-only. All write operations are written into the Snapshotfile - that means that the snapshot grows during this time in relation to the activitity of the VM / VDisk. Now the VDisk is mounted to the Backup Proxy running VCB which can now access and backup it. After this is finished the vdisk is unmounted from the backup proxy and the changes inside the snapshot file are commited to the real disk. The Snapshot is removed and everything is ok. So it always depends of the backup duration and VM diskactivity how big the snapshot will grow. I had cases where VCB did not properly remove the snapshot and it grew for days. So it might take some time to commit it. The Snapshot file is usualy stored with the vmdk files - however this can be changed if necessary.

Please note that VCB has quity a few limitations to consider when planning your Backup. For example:

Read-only access: you cant use the archive bit since the data on the vmdk can not be changed

Restore only via LAN, Backup via SAN

VCB Proxy must be able to access SAN LUN storing the vmdk files.

You might want to have a look at this document:

http://www.vmware.com/pdf/vi3_35/esx_3/r35/vi3_35_25_vm_backup.pdf

Kind Regards,

Gerrit Lehr

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Kind regards, Gerrit Lehr If you found this or other information useful, please consider awarding points for "Correct" or "Helpful".
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