vm creation

asked 2019-04-26 12:49:58 -0500

lelunicu gravatar image

hi, i like to see.

using glance image we can create a vm image that is stored in ceph server-if we use ceph.right/ when the vm is booted then in computer will be created an instance that is connected to the image in ceph.beside this an efemeral disk is created in computer local disk.right?the creation of this efemeral disk is compulsory? what is the purpose of this efemeral disk?is to keep swap and tmp? tnx

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answered 2019-04-26 17:13:11 -0500

updated 2019-04-26 17:35:57 -0500

The ephemeral disk contains the root filesystem and is a local file or a logical volume on the compute node, or is located on a storage system attached to the compute node, including a Ceph cluster or an NFS file.

Images can also be kept on Ceph. There are other backends like Swift.

You can launch an instance with a volume instead of an ephemeral disk.

An overview of the two types of instance storage: https://docs.openstack.org/nova/lates....

To configure ephemeral storage: https://docs.openstack.org/nova/lates.... rbd stands for RADOS Block Device.

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so when an instance is launched the os will be in a efemeral disk or in a volume.right?

lelunicu gravatar imagelelunicu ( 2019-04-26 23:59:04 -0500 )edit

Yes, exactly.

Bernd Bausch gravatar imageBernd Bausch ( 2019-04-27 00:12:47 -0500 )edit

it means that in efemeral disk case the application traffic uses only ram and local disk -in volume case the application traffic will goes over network from ram to ceph.right?

lelunicu gravatar imagelelunicu ( 2019-04-27 15:15:14 -0500 )edit

Your statement is only true if

  1. ephemeral storage is configured on a local disk and

  2. volume storage is configured on Ceph.

However, you can configure ephemeral storage on Ceph or an NFS server, and volumes can reside on other backends than Ceph.

Bernd Bausch gravatar imageBernd Bausch ( 2019-04-27 16:43:59 -0500 )edit

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Asked: 2019-04-26 12:49:58 -0500

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Last updated: Apr 26 '19