BrendanMarmont
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VDR - vDisk larger than 1TB

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Hi,

We have a file server which has a vDisk greater than 1TB. How is it possible to backup this VM with the limitation of being only able to mount a max 1 TB disk on the appliance?

Thanks in advance

Brendan

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DSTAVERT
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vDR isn't a suitable tool for backing up a disk that is that large. Even though the limit is 1TB in actual practice a 1TB isn't a good choice as a backup destination disk. Less than 500GB is a more appropriate choice and multiple 2 or 300GB even better. If something were to happen where vDR needed to re catalog a 1TB disk it may take days. I can tell you that re cataloging is not unusual. In the mean time you have no access to vDR. No backup takes place. Long and short -- find another tool to back up that disk.

-- David -- VMware Communities Moderator

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rievax
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Brendan,

Nobody even tried to answer your question...

First, having a 1TB virtual disk (.vmdk) means that your VMFS is  xxxxTB (bigger!)? In general, I don't think people have such big VMDK files: they prefer using RDM disk instead.

By asking the question, I think you answered already: either your original design with a 1TB vDisk is not good and / or VMDR is just not for this case. Use a different backup solution for that vDisk.

BUT, it may work: by using deduplication (and other compression techniques VMDR may have), it could possibly fit your vDisk on the target...

X.

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BrendanMarmont
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Thanks Rievax, so I gather our current setup is not best practice? The AKL_L1 LUN is using extent for a total provisioned space of 4TB.

Correct me if I am wrong - We need to create a new or assign an empy LUN of xTB, make that mapping availble to the vm via RDM, then migrate the data accross?

On a test vm, the RDM option is greyed out, I am making the assumption as above that the LUN has to be soley dedicated to a single vm before the RDM radio button becomes available?

Thanks for your time.

Brendan

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DSTAVERT
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Immortal

vDR isn't a suitable tool for backing up a disk that is that large. Even though the limit is 1TB in actual practice a 1TB isn't a good choice as a backup destination disk. Less than 500GB is a more appropriate choice and multiple 2 or 300GB even better. If something were to happen where vDR needed to re catalog a 1TB disk it may take days. I can tell you that re cataloging is not unusual. In the mean time you have no access to vDR. No backup takes place. Long and short -- find another tool to back up that disk.

-- David -- VMware Communities Moderator

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rievax
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Hello Brendan,

You should check the following: http://www.vmware.com/pdf/vsphere4/r41/vsp_41_config_max.pdf

Page 4 (top) shows your the maximum... To me, maximum means: "Please don't reach that!", but everybody has its own experiences. You are going to have the same limitations with RDM drives (2TB) but at least you don't have a virtualization layer in between.

I don't know anything about your infrastructure, but generally speaking 4TB LUN is pretty big and could be unmanageable if anything happens to the LUN or you OS partition. Ask yourself: how long do I have to recover a LUN if it goes down? We are not talking about home NAS with personal pictures and videos here... It you have a big 2TB VMFS LUN with 50 virtual machines on it and if your LUN goes down for any reason, you are going to loose all 50 VMs at the same time.

Again, everyone has its own preferences and experiences, but generally speaking, I think people tends to like having 500GB LUNs for their VMFS datastores and if you have to have bigger OS partitions for data, use RDM instead of VMDK: it make a cleaner job if you need to extend the partition later on. Google on the subject...

And yes, once you assign a new LUN to your ESX server, rescan the storage and the RDM option will be available to your VM.

X.

admin
Immortal
Immortal

VDR should not be used as a replacement for an enterprise backup solution. VDR is meant as a quick way to get critical VM's back up in the event of a loss. Using a proper backup solution is the correct answer here.

With that said I will go off on a tangeant and address some of the other things said here... There is nothing wrong with large VMDK files. There is nothing wrong with large datastores either. The 2tb limit is only due to supporting older filesystems. Using RDM's does not take the virtual layer out of the middle of things either. If you create an RDM in physical mode, yes it does bypass the vmkernel, but the layer is still there. The only reason to use an RDM at this point is if there may be a need for a physical machine to ever access the data directly or if you have an applocation that is SAN aware and will issue direct commands to the LUN. Best practices state that VMDK's are the way to go except for the two previous conditions. People may actually find that performance of a VMDK may be better than that of an RDM. The whole argument about separating the OS from the data is a throwback to pre-virtual times. Considering that the backing disks for a particular LUN are going to be the same, there's no need to split the OS from the data like in the physical world. In the physical world the OS would reside on a pair of mirrored disks and the data would be on separate physical disks to avoid contention. With shared storage it's all on the same backing group of spindles so the thought of separating these does nothing for performance anymore.