I am interested to see if you were able to get this resolved , as I am having issues as well . I have 3 worlds running on a virtual machine . Hardware is dual Xeon , 72 Gigs of ram , 6 x 4 TB drives in Raidz 2 , main OS just does ZFS and NAS functions , virtual machine 1 runs Plex Media Server , virtual machine 2 is Minecraft worlds . I have a creative world using 2 gigs of RAM , 1 CPU cores . It is slow , but I use it for small scale testing before building in survival typically . My survival world uses 48 gigs of RAM , and 5 CPU cores . This is what I mostly play on since my laptop can only handle Vanilla without mods . My ATM world uses 1018 gigs of RAM , and 6 CPU cores . I play on this from my desktop when I have time to play . I started the world over a few days ago after trying out mods for the first time ever . The world was also pregenerated to a radius of 6000 blocks from spawn in all directions , so chunk generation is not the issue . After reading some of the responses here , I believe I need to alter the way in which virtual machines run , as right now , they run off space in the RaidZ 2 pool . I have 2 brand new 120 gig SSDs I need to put in the box to replace the ancient 60 gig Agility 3 s that the main OS runs off of . Hoping that would in PART do the trick .