Hypervisor summary shows incorrect total storage

asked 2018-12-18 06:19:28 -0500

Am Ab gravatar image

Hello, I'm using a SAN storage as cinder backend and when create instance I can confirm the root disk will be created on SAN but Nova thinks it is created on Compute nodes. I found the disk usage in "Hypervisors" summary option in dashboard.

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answered 2018-12-18 10:34:32 -0500

reynoni gravatar image

What are the Ephemeral Disk sizes on the flavors you are using? From my understanding, openstack compute uses ephemeral disks on the compute node to start the instance, then uses the storage device designated as the drive.

I've got 0 GB as my ephemeral disk size and I show 0/9.7TB on my hypervisor screen.

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they are default openstack flavors, m1.small, ... medium, etc.

Am Ab gravatar imageAm Ab ( 2018-12-18 10:53:49 -0500 )edit

Okay. I think I get the disconnect. The local disk space it shows under hypervisors shows the storage that the compute hosts have on them locally, these are used by the ephemeral disks NOT your SAN backed instances. If you don't want to use ephemeral disks, you can set them to 0 like stated above.

reynoni gravatar imagereynoni ( 2018-12-18 12:43:22 -0500 )edit

But when I create an instance, the disk resides on San, I see them on SAN. The hypervisor summery will be increased as well. It is confusing...

Am Ab gravatar imageAm Ab ( 2018-12-18 13:13:17 -0500 )edit

Right, by default, the instance flavors have an ephemeral disk size that is non-zero, like yours, this creates a volume for the instance on the compute node SEPERATE from your SAN. Your SAN is probably working fine and that ephemeral disk might not even be used.

reynoni gravatar imagereynoni ( 2018-12-18 13:30:46 -0500 )edit

So to be clear, the hypervisor will create ephemeral disks even if it doesn't use them because that's what the flavor tells it to do. Then it registers that it created an ephemeral disk and add its storage space to it's total which is not your SAN instances.

reynoni gravatar imagereynoni ( 2018-12-18 13:45:19 -0500 )edit

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Asked: 2018-12-18 06:19:28 -0500

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Last updated: Dec 18 '18