Hi, All
I have done some work to test the performance of LUN scanning, use
"iscsiadm" with "--rescan" like what Nova dose. In my test, a host
connected with a lot of LUNs , more than 1000 LUNs. Because "--rescan"
will cause kernel to scan all of the LUNs connected to the host, it
costs several minutes to complete the scanning.

According to "connect_volume" at line 284 in nova.virt.libvirt.volume.py:
https://github.com/openstack/nova/blob/master/nova/virt/libvirt/volume.py#L252
Nova uses "iscsiadm" with "--rescan" to detect new volume, but this
command will scan all of the LUNs, including all the others which
already connected to this host. So if a host has a large number of
LUNs connected to it, the connect_volume will be very slow.

I think connect_volume needn't scan all of the LUNs, only need scan
the LUN specified by connection_info.

Is it necessary to discuss a more efficient way to improve this issues.

-- 
Best wishes
======================  Peter.W  ======================

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