[openstack-dev] [nova][cinder] Refactor ISCSIDriver to support other iSCSI transports besides TCP

Shlomi Sasson shlomis at mellanox.com
Wed Mar 26 12:36:06 UTC 2014

Hi Ramy,

There is quite a bit of difference between FC and iSCSI (e.g. iqn vs WWN ..)
While iSER is just an alternative iSCSI transport, and use the exact same tools on the initiator and target like iSCSI/TCP
Most iSER capable iSCSI targets don't even have a separate configuration for TCP or RDMA, and would accept both transports options on a given logical iSCSI target (why we don't need a different plug-ins for targets with exception of STGT)

On the initiator side the only difference between TCP and RDMA is in the interface flag (--interface=[iface])
e.g. "iscsiadm -m discoverydb -t st -p ip:port -I iser --discover"

so we don't need a full new class to propagate a simple flag, and rather make this a simple parameter
we also though of modifying the operation that "default_rdma" would mean try RDMA and if it fails fall back to TCP, to simplify operations.


From: Asselin, Ramy [mailto:ramy.asselin at hp.com]
Sent: Tuesday, March 25, 2014 17:55
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [nova][cinder] Refactor ISCSIDriver to support other iSCSI transports besides TCP

Hi Shlomi,

Another solution to consider is to create a subclass per transport (iSCSI, iSER) which reference the same shared common code.
This is the solution used for the 3PAR iSCSI & FC transports. See these for reference:

Hope this helps.


From: Shlomi Sasson [mailto:shlomis at mellanox.com]
Sent: Tuesday, March 25, 2014 8:07 AM
To: openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>
Subject: [openstack-dev] [nova][cinder] Refactor ISCSIDriver to support other iSCSI transports besides TCP


I want to share with the community the following challenge:
Currently, Vendors who have their iSCSI driver, and want to add RDMA transport (iSER), cannot leverage their existing plug-in which inherit from iSCSI
And must modify their driver or create an additional plug-in driver which inherit from iSER, and copy the exact same code.

Instead I believe a simpler approach is to add a new attribute to ISCSIDriver to support other iSCSI transports besides TCP, which will allow minimal changes to support iSER.
The existing ISERDriver code will be removed, this will eliminate significant code and class duplication, and will work with all the iSCSI vendors who supports both TCP and RDMA without the need to modify their plug-in drivers.

To achieve that both cinder & nova requires slight changes:
For cinder, I wish to add a  parameter called "transport" (default to iscsi) to distinguish between the transports and use the existing "iscsi_ip_address" parameter for any transport type connection.
For nova, I wish to add a parameter called "default_rdma" (default to false) to enable initiator side.
The outcome will avoid code duplication and the need to add more classes.

I am not sure what will be the right approach to handle this, I already have the code, should I open a bug or blueprint to track this issue?

Best Regards,

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