ESX SAN overbooked, what happens if storage limit reached?

Question

In ESX you can easily overbook the available storage with the Virtual Guests. What happens if a overbooked SAN reaches its capacity limit?

Its not an actual problem i'm faced with, we just had the discussion in the office and no one knows exactly what happens.

You're referring to "thin provisioning", right? – ewwhite Oct 01 '14 at 16:24 — ewwhite, Oct 01 '14 at 16:24

score 3 · Accepted Answer · answered Sep 30 '14 at 13:42

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By 'overbooked' do you mean overcommitted via the use of VMWare thinning? if so then what happens is that all reads stay good but any VMs that want to write can't - it's as simple as that, they get a SCSI 'block not available to be written to' error and have to deal with it however the OS/filesystem would do in that situation.

answered Sep 30 '14 at 13:42

Chopper3

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@ThomasSpycher This is incorrect. By "overbooked", I believe you are referring to "Thin Provisioned". [Thin Provisioned VMs will pause](http://www.vcritical.com/2009/10/easy-recovery-from-a-full-vmware-esx-datastore/) when they run out of datastore space. – ewwhite Oct 01 '14 at 16:23
Fair enough, I don't use it so was assuming it did what happens to physicals, good spot, I'll delete shortly. – Chopper3 Oct 01 '14 at 16:39
Damn, can't delete an accepted answer :( – Chopper3 Oct 01 '14 at 17:16

ewwhite · Answer 2 · 2014-10-08T12:42:14.863

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Your VMs will pause and say that there's no free space on the volume which the virtual machine(s) reside on.

When a datastore runs out of space, thin-provisioned virtual disks can no longer dynamically grow to accommodate additional storage demand. When VMware ESX detects this condition, virtual machines in need of additional storage are instantly paused to prevent guest operating systems from failing.

With video: https://www.youtube.com/watch?feature=player_embedded&v=4G8MEC14eKU

Edit:

This just happened to a remote domain controller this morning.

All services are down on node ewwhite - dc3. New Outage records have been created and service level availability calculations will be impacted until this outage is resolved.

enter image description here

edited Oct 08 '14 at 12:42

answered Sep 30 '14 at 13:44

ewwhite

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only if the virtual machine files are on the same storage as the vmdk – JamesRyan Sep 30 '14 at 13:45
But when i pause the VM, its current memory needs to get written somewhere? – Thomas Spycher Sep 30 '14 at 14:26
When I say "pause", I mean that VMware will stop the virtual machine. – ewwhite Sep 30 '14 at 14:27

score 0 · Answer 3 · answered Sep 30 '14 at 13:40

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It depends on the model of your storage array; generally the volume will go read-only or off-line, which will cause interesting problems to your VMs. Primarily shutdowns, in my experience.

answered Sep 30 '14 at 13:40

mfinni

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ESX SAN overbooked, what happens if storage limit reached?

3 Answers3