VMWare ESXi (version 4, I wonder about what ESXi 5 really brings) has a 2TB limit on datastore size.
So say you just bought a new Dell server and disk array, with let’s say 24 500gb disks, and wanna run it in RAID-6 for a total of 10230gb (22 * 465gb).
You’ll soon discover VMWare will limit the datastore to a little less than 2Tb. I’ll not go into the mess that is the reason for this, just accept it. Or buy ESXi 5 for US$ 10k.
One (poor) solution, would be to setup a few smaller RAID arrays (eg, four 5-disk 500gb RAID-5 arrays); each array totalling around 2tb, and create a few datastores, each with a little less than 2tb.
That’s bad because obviously you’ll waste a lot of disks; but it works.
The best solution is to make use of a little-advertised feature of RAID cards: disk groups. Since PERC 6 (PERC 6/i, PERC 6/E, H700 and H800) the card has 3 concepts: Physical Disks, Disk Groups, and Virtual Disks. Continue reading →