Looking at NetBackup 6.5 and the VCB integration looks pretty impressive. I'm familiar with VCB at a high level overview and the concern I've always had is that, I assume, I would need double the storage space for backups. I am utilizing SAN storage and with VCB taking a snapshot of the guest wouldn't that take double the space of what the storage is already using?
For example, say I have 1 guest that has a C: drive of 15GB. When the snapshot is taken for backup the storage space would then be 30GB (one real disk and one for the backup) right? If I extrapolate that out say I had 60 servers with 15GB C: drives, would I then need to plan SAN storage of 60 * 15 *2?
Am I thinking about this right? It seems to me it would be silly having to need double space but for some reason that's how I see it. Can someone either confirm or explain to me how this works?
Thanks.
No, a snapshot simply writes all I/O changes to a new file that starts out at 0 bytes and grows as necessary so it can read from the source VMDK. After the VCB exports the original disk image, it commits the snapshot to the existing image.
*EDIT* VCB mounts the Datastore read-only on the backup proxy so its not actually copying the original image off, only giving you read access to it and its files.
Message was edited by:
jjohnston1127
No, a snapshot simply writes all I/O changes to a new file that starts out at 0 bytes and grows as necessary so it can read from the source VMDK. After the VCB exports the original disk image, it commits the snapshot to the existing image.
*EDIT* VCB mounts the Datastore read-only on the backup proxy so its not actually copying the original image off, only giving you read access to it and its files.
Message was edited by:
jjohnston1127
So it's exactly how the snapshot feature works in Workstation then?
Yes.
Ok. Just to make sure I'm understanding this right.
HostA has 15GB C: drive in hosta.vmdk. When VCB starts hosta.vmdk is "frozen" and HostA starts writing to hosta.snapshot. VCB then does a backup on the "frozen" hosta.vmdk. Once the backup is completed hosta.snapshot is written back to hosta.vmdk and hosta.vmdk is "unfrozen"
Did I get that right?
Yep, that's exactly correct. The process anyway. It's not actually a .snapshot file extension but the concept is correct
Yeah, was just using .snapshot for the example.
Thanks for your help in letting me understand this. It definatelly seems like an amazing option now that I realize when they say "snapshot". It's not a SAN snapshot per say but a snapshot like workstation has.
Thanks again!
Still you should atleast have 10% of free space per VMFS volume. And you would need extra diskspace on your VCB Proxy, cause it will temporarily hold the vcb dumps.
Yeah, we have plenty of free space on the VMFS volumes -- just not double the free space that I thought we might have needed. Thanks.
besure to disable automount on the vcb proxy before you go, otherwise your vmfs volumes will be windows toast.