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dynamic iSCSI target discovery for ucs blades

We follow UCS best practice and use iSCSI booting for all our b200 blades and c2xx servers. This works great as we can boot any profile on any B200 and boot iSCSI LUNs follow the profile. We use static target settings for the boot LUNs pointing to the Netapp SVM IP and IQN. We plan to deploy Disaster Recovery for our NetApp replicating all the volumes and LUNs to the second Netapp. The standby Netapp will come on-line in case of disaster on the same IPs as the first one. The issue is the IQN of the ISCSI targets – the second Netapp is different. I would like to use the second method of iSCSI target configuration – the dynamic target discovery – that uses just an IP of the target. UCS Manager has two options: static-target-if and auto-target-if. The first is very well documented in the UCSM server management guide. The second is a mystery. The description instructs to use DHCP option 43 with ‘vendor id’ and nothing more. I assume DHCP option will include the iSCSI target details. There is no word on what they are and how they are used.
I assume that the UCS iSCSI boot with auto-target-if mode would follow something similar to Linux ISCSI module using root-path DHCP option. Is there a UCS auto-target-if HOWTO somewhere?

 

For these that I lost in my description here is UCS CLI showing details of both iSCSI target modes. We use static-target-if but want to use auto-target-if.

top
scope service-profile server 1/6
scope iscsi-boot
scope vnic-iscsi iscsi_1
scope static-target-if 1
show
up
scope static-target-if 2
show

Static target:
Priority Name Port Ip Address Auth Name
-------- ---------- ---------- --------------- ---------
1 iqn.1992-08.com.netapp:sn.30b48e78556d11e9b39200a098f677f8:vs.20
3260 10.5.53.24
Static target:
Priority Name Port Ip Address Auth Name
-------- ---------- ---------- --------------- ---------
2 iqn.1992-08.com.netapp:sn.30b48e78556d11e9b39200a098f677f8:vs.20
3260 10.5.53.25

 

top
scope service-profile server 1/5
scope iscsi-boot
scope vnic-iscsi iscsi_1
scope auto-target-if
show


Auto target:
Dhcp vendor id
--------------
iscsi1

 

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2 REPLIES 2
Cisco Employee

Re: dynamic iSCSI target discovery for ucs blades

Greetings.

In looking around at the RFC, https://www.ietf.org/rfc/rfc2132.txt, it seems like you may also need to set option 60 with same value.

For option 43, I think it is in the sub-option definitions (i.e. 201,202,203) that you will actually define iSCSI target info, iSCSI initiator IQN, etc.

 

When checking Netapp docs, https://mysupport.netapp.com/NOW/public/eseries/sam/index.html#page/GUID-8538272A-B802-49D9-9EA2-96C82DAD26A2/GUID-AAB258D5-EC18-4D40-9A3D-264ACC94BFBF.html , it appears that maybe just the option 43/60 setting is sufficient if you have a iSNS server to help facilitate the iqn and session discovery.

 

Sorry, don't see a lot of info on this either.

 

Kirk...

 

Re: dynamic iSCSI target discovery for ucs blades

Thanks for the pointer to the RFC2132.  It describes the option 43 briefly and explains that vendors must define their own sub options and their semantics so when the DHCP server responds with them they comply to what vendor (in this case Cisco) needs.  I don’t see anywhere the sub-options 201,… - where did you find that?  This is what we are missing in the UCS manuals.

As to Netapp dynamic target discovery mode – this is a default mode – as we are using it in ESXi to dynamically discover iSCSI datastore LUNs just by the Netapp IP.

 

A good example of the option 43 use is in the ISC DHCP manual for Sun microsystems SUNW at: https://www.isc.org/wp-content/uploads/2017/08/dhcp41options.html#VENDOR%20ENCAPSULATED%20OPTIONS

 

option space SUNW code width 1 length width 1 hash size 3;
option SUNW.server-address code 2 = ip-address;
option SUNW.server-name code 3 = text;
option SUNW.root-path code 4 = text;

 

We need that for Cisco UCS iSCSI booting process.

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