Hi,excuse me,about the number of target and lun.

[letterwuyu]

Now I find that I can only create a target and create a maximum of 256 Lun, and I want to ask if there is a way to create more Lun.

[dillaman]

No, 256 LUNs per target is a limitation within LIO I believe.

[letterwuyu]

@dillaman thank you for your answer and great work, I have another question： As I have just mentioned, a iSCSI gateway cluster can create only one target. Can I create two target by creating two iSCSI gateway clusters (connecting the same CEPH cluster), thereby increasing the number of Lun support?

[dillaman]

@letterwuyu What's your use-case for needing such a high number of LUNs?

[letterwuyu]

@dillaman At present, we want to use CEPH to do the back-end storage of VMware, and later it will be used for other businesses. Considering the expansion problem, I don't know whether the 256 number can meet the general needs, so I want to know about it.

[dillaman]

@letterwuyu For the VMware case, I don't see why you would need so many LUNs. You would only need to export maybe one for each gateway to spread the load appropriately. VMware will put its VMFS on top of the LUNs to build a single datastore over the LUNs. If you need to add more space in the future, you can resize the LUNs.

[letterwuyu]

Yes, VMware case is what you said. Thank you very much for your detailed answer.

[mikechristie]

Just a FYI.

rtslib was fixed the other day to support more luns:

https://github.com/open-iscsi/rtslib-fb/commit/20a50d9967464add8d33f723f6849a197dbe0c52

There is still a problem where older kernels like used by RHEL 7.4 only support 256 due to a hard coded limit in the kernel (this is fixed in RHEL 7.5 btw). Newer kernels are limited by the SCSI spec and what a 64 bit id can hold and what your system can allocate before it runs out of memory :)

If there is a need we can update our tools. Note that vmware only supports 512 LUNs for iscsi so you normally do what dillaman suggested. Maybe we should just at least increase our limit to match vmware.

[letterwuyu]

oh, thanks for your FYI

[zhuozh]

I'd like to add an additional usecase. Openstack baremetal case also require higher number of LUNs.

[dillaman]

@zhuozh That's not really a use-case we plan to work on, but contributions are welcome.

[sadiq1425]

I need to create 2 targets in iscsi gateway The use case is for creating differenrt target for self hosted engine storage doamin and another for additional storage data domain . Can you suggest me a solution for this . Thanks

[dillaman]

You can map different LUNs (RBD images) to different initiators within the same target. That will allow you to have isolated storage domains.