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Hi, Kim KS:
	"cross_az_attach"'s default value is True, that means a llow attach between instance and volume in different availability zones.
	If False, volumes attached to an instance must be in the same availability zone in Cinder as the instance availability zone in Nova. Another thing is, you should care booting an BFV instance from "image", and this should interact the " allow_availability_zone_fallback" in Cinder, if " allow_availability_zone_fallback=False" and *that* request AZ does not in Cinder, the request will be fail.


About specify AZ to unshelve a shelved_offloaded server, about the cross_az_attach something you can know
https://github.com/openstack/nova/blob/master/releasenotes/notes/bp-specifying-az-to-unshelve-server-aa355fef1eab2c02.yaml 

Availability Zones docs, that contains some description with cinder.cross_az_attach
https://docs.openstack.org/nova/latest/admin/availability-zones.html#implications-for-moving-servers 

cross_az_attach configuration: https://docs.openstack.org/nova/train/configuration/config.html#cinder.cross_az_attach 

And cross_az_attach with the server is in
https://github.com/openstack/nova/blob/master/nova/volume/cinder.py#L523-L545 

I am not sure why you are need " enable_az_attach_list = AZ1,AZ2" configuration?

brinzhang


> cross_az_attach
> 
> Hello all,
> 
> In nova with setting [cinder]/ cross_az_attach option to false, nova creates
> instance and volume in same AZ.
> 
> but some of usecase (in my case), we need to attach new volume in different
> AZ to the instance.
> 
> so I need two options.
> 
> one is for nova block device mapping and attaching volume and another is for
> attaching volume in specified AZ.
> 
>     [cinder]
>     cross_az_attach = False
>     enable_az_attach_list = AZ1,AZ2
> 
> how do you all think of it?
> 
> Best,
> Kiseok
>