vSphere ESXi – Copying VMs – what you may not know
So this article is more of a FYI than anything. I wanted to just bring some attention to this as some may really be puzzled by why the hypervisor stinks at performing large copies. @Lamw can verify as well especially when working the VM Disk files. I think it is important to highlight the distinct difference. The CP command is for files (although a VM by definition is a subset of files per VMware) but not the VMDISK files. I am sure there can be much conspiracy for why this is the case but this has actually been around for a while. If I was probably one of the age old VMware guys out there this would probably not catch me off guard because it has been around or published I should say since VI3 (ESX 3). So obviously since I did not finish my Back to the Future Delorian ride in time yet, well I just didn’t know.
During a particular situation I was copying some data from one ESX to another. This was basically a copy using the Datastore Browser in the vSphere client. I had staged some files from a NFS mount and wanted to copy them over to the SAN datastores. This NFS mount was read only so doing a storage migration would not work because they would require removing the VMDK files on the NFS mount after the copy. So I could do some clones but I could only do so many at a time. What I decided was to pop open the datastore browser and do a copy paste from the NFS to the SAN datastore. It’s also important to understand that the Datastore Browser uses HTTP GET and PUT not CP. Keep in mind this is over 10GB Ethernet (NFS) and copying to the SAN which is 4GB FC HBA. It took a while to do the copy but I didn’t really notice. After staging all the data to the new SAN datastore I had to then turn it over to another ESX that had yet another separate datastore from the one hosting all the VMDK files. So there again another copy…. This time I noticed how slow it was really going even from datastore to datastore. I knew that the copy process would more than likely run over the Management Interface but even that was on a 10GB Ethernet connection so that should be screaming as well. Not the case… So as a last test I decided to try a copy from Datastore to Datastore that is mounted to the same host. I still averaged around 20-50kbs which is pretty terrible. So no matter how I went about it performance was terrible. I pretty much knew it had to do with the process at this point although I wasn’t sure why. In many of these scenarios I used different methods from SCP applications, the Datastore Browser, and CP in the shell of ESXi.
Trying a Different Approach
So after talking with VMware support and confirming my suspicions on the issues being around the process (using CP) we went through the very same instances I noted above to rule out any issues. We tested the same scenarios; Different Protocol Datastores, Non-shared Datastore copies, Shared Datastore Copies, Local Datastore to Datastore copies, all with the same affect – even when copying just a single disk. Of course at this point the support guy was a little stumped and had to get off the line to go talk to someone else. Usually that means they need to go to someone with a fresh set of eyes or more experience to help out and sure enough he came back with another suggestion; use cloning and storage migrations as a test. I of course didn’t think of this but when he mentioned it I pretty much had a Homer the Simpson “DOH!” moment. I guess by then my head was hurting trying to figure this stuff out. When we did the storage migrations and clones it was actually MUCH faster. In fact after the support call we did some testing. I could do 10 storage migrations to 1 VM copy using the CP command. In some cases it was 10+ to one VM copy. Granted I had to now have an additional step of adding to inventory the VM Guest but that wasn’t as bad as taking 1 hour to copy 1 virtual machine. Note: The array was not VAAI capable
What does this mean?
Yeah, so that is the million dollar question isn’t? Well CP has pretty much been deprecated since VI3 but its better said “Not to be used for handling Virtual Disk”. To better understand see/read for yourself: http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&docType=kc&docTypeID=DT_KB_1_1&externalId=1000936
In http://www.vmware.com/pdf/esx_3p_scvcons.pdf page 3
NOTE:notice the words “SIGNIFICANT PERFORMANCE IMPROVEMENTS”
So all this to tell you that CP is not a very good solution for doing mass copies or datastore copies. For me this present a problem when using any other tools like VEEAM SCP, Putty SCP, and etc.. So make sure you know what you want to accomplish beforehand as you don’t want to end up with some headaches as I did. I know that some of you may think it was a waste of a VMware case but anytime I can find information like this and share it out for others for me is invaluable. To add to my findings I should also mention that VMKFSTOOLS also ensures the integrity of the disk and is more suited for these things by design. I think VMware intentionally focused on VMKFSTOOLS as the solution because I don’t think CP was ever something intended to be used due to the lack of functionality. It may have some to do with licensing as well.
One Last Thing:
This was a huge pain at the time of moving some data between the NFS and SAN because I really didn’t have an automated solution for doing the copies. Many of you know that VEEAM FAST SCP before the new version did not have 64-bit support. I didn’t have any 32 bit machines and I didn’t want to waste time hacking away. However, I did want to mention that VEEAM released their new version of the product which is known as VEEAM free backup; you can get that here. I also did some testing and was very impressed with the copying speeds compared to that of the CP command. Another nice thing is that even if you have no Virtual Machines registered in the vCenter it still picks them up in the copy process as VMs. Not to mention you can get statistics and automate-schedule copy jobs with the application. For me and with what I do this is priceless. Simplicity, automation, and reporting – all free! I love it! Thanks to VEEAM for listening to all those out there wanting an improved solution. They did a good job. NOTE: Thanks again to @Lamw for pointing this out. The Datastore Browser uses HTTP Get/Put not CP. I will correct this in the post later.
Posted on June 20, 2012, in ESXi, Troubleshooting, vOperations and tagged command, copy, cp, cp command, esxi, management interface, nfs mount, service console, slow. Bookmark the permalink. Leave a comment.