Disk.SchedulerWithReservation aka mClock

A long time ago when playing around in my lab with vSphere 5.1 I stumbled across this advanced setting called Disk.SchedulerWithReservation. I start digging to see what I could do with it and what it was about… if I could anything with it at all.

The description was kind of vague but it revealed what this disk scheduler was, it mentioned “mClock”. For those who don’t collect academic papers for night time reading like me, mClock is a new disk scheduler which is being researched by VMware and partners. The disk scheduler, in contrary to the current scheduler SFQ, will allow you to do some more advanced stuff.

For instance mClock will allow you to set an IOps reservation on a VM. So in other words, when you have a virtual machine that needs to have 500 IOps guaranteed you will be able to do so with mClock. Now I have been digging and asking around and unfortunately this logic to set reservations has not been implemented in 5.1.

If you are interested in mClock and its benefits I would recommend reading this academic paper by my colleagues Ajay Gulati (One of the leads on: DRS, Storage DRS, SIOC). I find it very interesting and hope it will be fully available sometime soon. And before you ask, no I don’t know when or even if this will ever be available.

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