The musings of an IT Consultant

Oct 31 2009   8:11PM GMT

How much free space is needed on a LUN for VMware?

Raj Perumal Raj Perumal Profile: Raj Perumal

Hi folks! One of the common questions you might find in the virtual world with VMware is how much free space do I leave on a LUN? When is it not enough?

A common mistake is to think you only need enough free space for the size of the VM itself and not much more. Well if you do that you’ll quickly find out the hard way that you should have allocated more. You see VMware needs space for things such as snapshots and space for emergency situations where you might need the space for shuffling things around from LUN to LUN.

The general consensus for free space on a VMware LUN is 10% to 20% free space. This isn’t just for snapshots, but also to account for any emergencies you might have to deal with on a VM where you need the free space. So if you don’t have  10% to 20% free space, then essentially you should treat the disk as full for all intents and purposes. 20% can be considered on the conservative side but it doesn’t hurt to be cautious.

I have heard people say 10% to 15% is good enough but only if you have very strict snapshot policies to ensure that you are monitoring the disk space closely.


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