[openstack-dev] [Nova]libvirt: connect_volume scans all LUNs, it will be very slow with a large number of volumes.RE: [OpenStack][Nova]May be performance issues of connect_volume in Nova

Wangshen (Peter) peter.w at huawei.com
Thu Aug 28 09:47:46 UTC 2014

Hi, All
I’ve reported a bug related to this mail: https://bugs.launchpad.net/nova/+bug/1362513

From: Joe Gordon [mailto:joe.gordon0 at gmail.com]
Sent: Wednesday, August 27, 2014 1:12 AM
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [OpenStack][Nova]May be performance issues of connect_volume in Nova

On Tue, Aug 26, 2014 at 5:36 AM, Wang Shen <ws1210 at gmail.com<mailto:ws1210 at gmail.com>> wrote:
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<http://nova.virt.libvirt.volume.py>:
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.

It sounds like this is a bug; we use https://bugs.launchpad.net/nova to track bugs so they don't get lost.

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

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