If you wanted Time Machine to work with a SMB share you will notice that it doesn’t work. To get it to work run the following command on the terminal

defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1

Now mount your SMB share. The best way to do this is to click on Go->connect to server in the finder menubar. For the server name you enter smb://username:password@servername/ShareName. I have a NAS share which has a Guest account with no password so my address looks like smb://Guest:@MyServer/HomeShare/TimeMachineBackup. Notice I have no password as no password is required for the Guest account.
Once mounted, Control click on the Time machine in the Dock and select “Time Machine Preferences”. Once you select “Choose Backup Disk” you should see your SMB Share. Select your SMB share and start your Time Share.
Once Time Machine backup starts, you will see an error saying that it cannot create image error. This error message was expected as Time machine could not create a file called a sparsebundle which is required for it to work on the SMB share. For this to work correctly we will be creating the sparsebundle manually. Turn off Time machine and go on to the next step.

In your terminal find your mac address. You can do this with the following command

ifconfig en0 | grep ether

Make a note of the mac address without the colon symbol. For this example lets assume my MAC address is 000000000000. Decide on how big you want your Time Machine backup to be. Then run the hdiutil command to create your sparsebundle file. Here is the command I created for a 200 Gigs share -

hdiutil create -size 200g -fs HFS+J -volname “OSX Backup” mymac_000000000000.sparsebundle

Where 000000000000 is my mac address and mymac is my mac name.

Now copy the sparsebundle file to the Nas share you want for your backups. In my case I copied it to the TimeMachineBackup folder on my NAS Share.

Go back to Time machine preferences and turn on Time machine. You should now see that the backup starts up with no problems. Depending on what you are backing up, the first time it runs it might take some time.

An important point to note is that for this to work your NAS Share needs to be mounted. You can set Time machine to be manual so that way you can make sure your SMB share is mounted before you click on the backup button.