jpoling
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VCB, again

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I may have missed it in the documentation, but can someone provide me with the following requirements:

1. How much space is required on the VMFS volumes for the snapshots that VCB creates?

2. Is storage space needed on the proxy as well for snapshots? If so, how much space approx?

Thanks,

Jeff

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enDemand
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To clarify a bit more...

The VMware snapshot process is used to make VCB possible. VMware snaphost are not full copies of the VMDK, so for all intents and purposes, they don't consume much space. Especially when they are only used for a short period of time (such as the time to backup your VM). When VCB invokes the snapshot, it creates a redo file (or delta log file) for each virtual disk to capture new write I/O destined for that disk. The initial file size is 16MB and it grows in 16MB increments. So depending on what write I/O the VM experiences while the VCB-based backup is running, that file can remain small or grow considerably.

Also remember that after the backup, VCB merges the delta back into the VMDK. So if the delta grew large, this may take a while and will add considerable I/O to your VMFS datastore.

Rule of thumb, then...schedule your high I/O activities (other than the backup itself) outside of your VCB window for that VM. This should keep the delta size relatively small and also speed up post-VCB, or "thaw", activities to a minimum.

If you find this or any other answer useful, please consider awarding points by marking the answer "correct" or "helpful".

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nitinsahi
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Hi Jeff,

You will find the answer here in these links with the whole process.

http://www.commvault.com/pdf/CommVault_VCBCertificationKit.pdf

http://vmzare.wordpress.com/2007/02/16/vmfs/

Nitin

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jpoling
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Maybe I need to clarify my initial question (after reading documentation from our backup vendor and Vmware).

It seems that in order to backup using VCB, I need space for snapshots.

--Does VCB require that space to be on the VMFS volumes or on the VCB proxy or both?

--If snapshots are created on the VCB proxy, does it need an amount of disk space that is identical to the size of the VMs vmdk files?

Thanks,

Jeff

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bjmoore
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Maybe I need to clarify my initial question (after

reading documentation from our backup vendor and

Vmware).

It seems that in order to backup using VCB, I need

space for snapshots.

--Does VCB require that space to be on the VMFS

volumes or on the VCB proxy or both?

--If snapshots are created on the VCB proxy, does it

need an amount of disk space that is identical to the

size of the VMs vmdk files?

Thanks,

Jeff

You'll need the "normal" amount of space in your VMFS volumes for snapshots, which is just the additional size of the redo file that it makes to temporarily write changes to. This should be really small, unless you're writing a lot of data to a VM or you have it snapshotted for an extended period of time.

If you do a file-level backup of VMs, you won't need extra space on your VCB proxy (because it mounts the drive letters like a mapped drive).

If you do a FullVM snapshot of the VMs, you'll need the total size of the VMDK file, minus any whitespace that may exist. A VMDK file sized at 10GB but only using 5GB would only need 5GB.

-Ben

jpoling
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Thanks for the clarifying info. I appreciate it

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bjmoore
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No problem. You may want to look at my post below called "Custom VCB script," which contains a custom vb script to simplify VCB/backup integration.

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enDemand
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To clarify a bit more...

The VMware snapshot process is used to make VCB possible. VMware snaphost are not full copies of the VMDK, so for all intents and purposes, they don't consume much space. Especially when they are only used for a short period of time (such as the time to backup your VM). When VCB invokes the snapshot, it creates a redo file (or delta log file) for each virtual disk to capture new write I/O destined for that disk. The initial file size is 16MB and it grows in 16MB increments. So depending on what write I/O the VM experiences while the VCB-based backup is running, that file can remain small or grow considerably.

Also remember that after the backup, VCB merges the delta back into the VMDK. So if the delta grew large, this may take a while and will add considerable I/O to your VMFS datastore.

Rule of thumb, then...schedule your high I/O activities (other than the backup itself) outside of your VCB window for that VM. This should keep the delta size relatively small and also speed up post-VCB, or "thaw", activities to a minimum.

If you find this or any other answer useful, please consider awarding points by marking the answer "correct" or "helpful".

View solution in original post

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jpoling
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Thanks for the detailed information!

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