I also wanted to use the 8.1 simulator and gave up just at the unzip process. In case I saw it correctly, you'll need at least 300 gb of free space on your harddisk. Netapp switched to use flat files for all the harddisks in the simulator rather than non-fixed drives.
Message to Netapp: Would be nice of you not to flat-file the harddisks ....
Well - I had another try yesterday, downloaded vsim-DOT811-7m.tgz and wanted to unzip it. I needed to stop it at round about 200 gb because I don't have more space on my disk. In case the harddisk files in there would be really thin provisioned, the unzipping would be smooth. But the files are flat and so I really need a lot of storage to have a successful unzip process. Only after unzipping I can follow the instructions at the link you provided.
For the older versions of the simulator you have thin provisioned disks. 8.0.3 needs only 48 gb on the harddisk. Would be nice to have it like that for the newer versions 8.1 and 8.1.1 too.