Thanks Ken - been on the road all day making the company some money ;o)

Dave

Still, since the vendor' documentation of the new feature is practically non-existant, can someone summurise the requierements for the proxy helper machine please. Particularly the details like network connectivity; local disk/s ( and the stores it belong to); scsi controller configuration etc. Does anyone have a working setup he can comment on/share details of?

Does "shadow copy" means dummy VM --- something existing in perception.

Duncan,

Can you please get some details about exactly how this "hot-add" mode works? Since it requires a helper VM, I'm assuming the VCB Proxy is using the helper as a stub for hot-adding the .vmdk of the VM to be backed up. Since you have hot add capability, but not hot remove capability, the helper provides the stub that can be power cycled to release the reservation on the source .vmdk. This all makes some sense to me, but it raises an important question: If the VCB Proxy is able to use another VM (albeit an empty one) to proxy disk drives, what protections are available to prevent someone from using whatever technology enables this "trespassing" between VMs for a nefarious purpose?

Ken Cline
Technical Director, Virtualization
Wells Landers
TVAR Solutions, A Wells Landers Group Company
VMware Communities User Moderator

I had decided to install VCB in a physical server, until today I run into this "SCSI hot-add mode" (and the fact that the VCB proxy is now supported in a VM) and I am reconsidering my options. First of all, why is it called SCSI hot-add mode, when it seems like it can be used in a NAS environment? I quote from the latest version of the VM Backup Guide, from the "SCSCI hot-add mode section": "In this mode, you can use Consolidated Backup to protect any virtual disks on any type of storage available to your ESX Server host, including NAS or local storage." It also states: "Although this mode is not as efficient as the SAN mode, which does not cause any overhead on the ESX Server host, it is still more efficient than theLAN mode." If the shared storage in question is a NAS, how is this hot-add mode more efficient than the regular LAN mode? Under the "LAN mode (NBD mode)" section it states that the VCB proxy can be either in a physical server or a VM. So in the case in which the shared storage is a NAS, I see no difference between the hot-add mode and the LAN mode. What am I missing?

Like someone else that contributed to this discussion, I also will not implement this new hot-add feature in VCB unless more thorough documentation is made available. But aside from the documentation, I have one more doubt about how having VCB in a physical server vs. a VM compares. I am concerned with the speed with which backups take place. I have 2 ESX hosts with 4 VMs each. Some VMs have their data store in the NAS, some in the local ESX hosts. I intended to install VCB in a physical server, and connect to this server external hard drives via an eSATA connection. I intended to copy the vmdk files straight into this external drives, which I would rotate during the week and take off-site for the sake of off-site backups. If I have VCB in a VM, I suppose I could copy to external drives that are attached to a physical server in the network that has a share for the external drive. Can someone help me understand how the speed with which backups would take place compares in each scenario? If VCB is in a VM, the transfer of data from the ESX host to the VCB proxy happens within the ESX host virtual network, then the copying of the data to the external drive happens over the LAN. If I have a physical server for VCB, the transfer of the data from the ESX host to the VCB proxy happens over the LAN, but the writing of the data to the external drives happens over an eSATA connection (3GBits/second). My VMs' virtual disks are 40 to 50 GB average. The LAN transfer speed would be 1GBit/sec.

Finally, I would greatly appreciate some feedback on the backup schedule I intend to implement. Does anyone see any problems with only doing backups of the full VM images every day, and no backups of specific data files? I suppose the other alternative is to do data file level backups daily and maybe full image backups weekly or so, mainly for disaster recovery purposes. But from a management point of view, it seems to me it would be much simpler to just backup the entire VMs every night and not mess with file-level backups. Any thoughts on this?

Thank you so much in advance for any thoughts anyone cares to share. I am pretty new to VMware and I could use advice from others with more experience.

PS: I am running VirtualCenter 2.5 and VI 3.5

Marcelo

Macelo -

First, Welcome to the forums!

As for the operation of the Hot-Add mode (As everyone says, documentaion is sparse at best and some theories may be changed after the next doc update) The way I understand it, The "helper VM" has the vdisk to be backed up "hot-added" to it. It is called "SCSI" Hot-add, because the vdisk is presented as a SCSI disk. Just like a VMDK on the NAS or FC SAN is presented as a SCSI disk to a regular VM. In order to use VCB to back up a VM, thedisk must be a vdisk. It doesn't matter if the VMDK or RDM is on a NAS, FC SAN, iSCSI SAN or local disk. The key is that it need to be in virtual compatability mode so a snapshot can be taken.

As for throughput, the process is VERY I/O intensive. I have done numerous throughput tests and with a 4GB FC SAN, the best I can get is about 1GB per minute of data throughput for each channel. I have never done timing tests on GbE NAS or iSCSI. It would be more efficient in hot-add mode as opposed to nbd mode because the I/O is at "backplane" speed instead of network speed. The trade-off is that it is one more thing the COS is doing. In your case, it sounds like your VMDKs are on NAS. The decision or physical vs. VM is purely money. Do you really need a separate server when a VM can do it just as well?

The trick with using a VM is where you will place your backups, and ultimately, how are you going to put it on tape....

Dave

Well, I got hot-add working too....but only for VMs with a single VMDK -- my VMs that have multiple VMDK files crap out. The error is; date/time 'vcbMounter' 3504 error Error: Failed to hot remove SCSI disk: Incompatible device backing specified for device '1'.

ideas?

~Rick
VMwareTips.com