Friday, 1 July 2011

Veeam VMWare network restore speed

Whilst most of VMWare is very fast and efficient copying files in and out of the datastore is depressingly slow - you are lucky to get 10 MB/s even with fast hardware and gigabit network, I normally get closer to 5 MB/s.  There is a trick you can use with Veeam restores over the network to vastly improve this speed, something similar should work if you are using shared storage but I can't test this myself.

The problem is basically the slow network performance when copying files to or from the datastore over the network.  There are a lot of people talking about this online and it has been an issue with VMWare since at least version 3.5 (4.1 made some small improvements).  At 5MB/s a large VM  can take ages to copy - especially as it transfers the full image over the network.  So if you have a VM with a "thin" hard disk format, 200 GB in size but with only 10GB of data it will take 10GB on the datastore.  When you try to copy it to your desktop it will transfer 200GB over the network.  The code that deals with migrating datastores, storage vMotion etc is all really fast so people with higher end setups will not use this feature much.  Also if you have a SAN you can just upload direct to the SAN then connect it to VMWare - not possible if you are using local storage...

This faster code is the way to get big VM's onto ESXi quickly using Veeam.  First you need to do an "Instant Recovery".  This sets up the VM on the destination ESXi host but also shares a folder from the Veeam server containing the backed up image.  Restoring this instant recovery takes seconds regardless of the size of the VM.  However the files themselves are still stored on your backup server.  If you were to turn on this instantly recovered VM it would be running from files over the network - probably a bit slow and not what you really want to do long term.  However if instead you right click on the VM in vSphere you can choose to migrate - follow the wizard and tell it to change the datastore.  Moving the files from the temporary backup datastore to your main datastore like this runs as fast as your hardware supports - probably at least 20MB/s even on fairly normal servers as long as you have GB network cards in use.

Hopefully VMWare will fix this soon as it takes a bit of googling to find out why restores take so long with Veeam and find  a workaround - I'm sure many people just give up.  This same problem makes backing up a VM from the free ESXi hypervisor a very slow process, which might be putting people off from buying the program.

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