Your enterprise’s mileage may vary, but in every place I’ve ever worked at, I’ve taken a pretty dogmatic approach to disk space utilization on VMs, especially ones hosting specialty workloads, such as Engineering or financial applications.
And that dogma is: No workload is special enough that it needs greater than 15% free disk space on its attached volume, non-boot volume.
This causes no end of consternation and panic among technicians who deploy & support software products.
“Don’t fence me in!” they shout via email. “Oh, give me space lots of space on your stack of spindles, don’t fence me in. Let me write my .isos and .baks till the free space dwindles! Please, don’t fence me in,” they cry.
“I can’t stand your fences. Let my IO wonder over yonder,” they bleat, escalating now, to their manager and mine.
Look, I get it. Seeing that the D: drive is down to 18% free space makes such techs feel a bit claustrophobic. And I mean no disrespect to my IT colleagues who deploy/support these applications. I know they are finicky, moody things, usually ported from a *nix world into Windows. I get it. You are, in a sense, advocating for your customer (the Engineering department, or Finance) and you think I’m getting in your way, making your job harder and your deployment less than optimal.
But from my seat, if you’ve got more than 15% free space on your attached volume in production, you’re wasting my business’ money. I know disk space is cheap, but if I gave all the specialty software vendors what they asked for when deploying their product in my stack, my enterprise would :
- Still have a bunch of physical servers doing one workload, consuming electricity and generating heat instead of being hyper-rationalized on a few powerful hosts
- Lots of wasted RAM & disk resources. 400GB free on this one, 500GB free on that one, and pretty soon we’re talking about real storage space
One of the great things about the success of virtualization is that it killed off the sacred cows in your 42U rack. It gave us in the Infrastructure side of the house the ability to economize, to study the inputs to our stack and adjust the outputs based not on what the vendor wanted, or even what us in IT wanted, but on what the business required of us.
And so, as we enter an age in which virtualization is the standard (indeed, some would argue we passed that mark a year or two ago), we’ve seen various software vendors remove the “must be physical server” requirement from their product literature. Which is a great thing cause I got tired of fighting that battle.
But they still ask for too much space. If you need more than 15% free on any of the attached, MPIO-based, highly-available, high performing LUNs I’ve given you, you didn’t plan something correctly. Here’s a hint: in modern IT, discrimination is not only allowed, but encouraged. I’m not going to provision you space on the best disk I have for backups, for instance. That workload will get a secondary LUN on my slow array!