Ive seen a lot of HDS Enterprise implementations where only one host type is assigned to a port such as -
CL1-A - HP-UX hosts
CL1-B - AIX hosts
…
..
And the people who designed and manage these environments can get quite religious about not mixing host types on the same port.

Im aware that you can mix different host types on a port using HSDs, but are there any performance or other advantages to not mixing different hosts types on the same port?

Strangely none of these people have ever been able to give a valid reason for this and I just assume that its something they have carried over from other vendor implementations.

Thanks in advance
PS. Great blog

Hi Alex. There are many levels of mode setting, and one platform may have several depending on configuration differences like clustering. SUN and Windows can share the same mode setting in some cases as you point out. In our systems we give them different mode settings.

There are actually four places you can do LUN masking. In addition to the server, you can do it at the storage port or at the LUN level. In our case we add a fourth level which is a Host Storage Domain, HSD. In a storage controller without an HSD you can only do it at the Port or LUN Level. While LUN level masking may seem to have an advantage since it is more granular, it adds to complexity. With HSD, we mode set the HSD then drop LUNs into the HSD without having to mode set or mask each LUN. Each HSD is a separate address space so each HSD can see LUN 0 and assign LUNs consecutively. This helps to reduce the complexity of LUN management.

I admit that I am not an expert or a user of other vendors storage, so please let me know how others are doing this.

I agree that this is not a key feature, compared to the other features in our storage systems, but I believe it is a differentiator in our overall virtualization solution.

Most storage systems I know support differents types of hosts, which are assigned to host-adapters WWN’s. Solaris and Windows hosts can be attached to the same physical port and have different address spaces (LUN’s). This is true for all midrange disk arrays I know and even for some low end boxes.

So I still don’t see any advantages, basically you do exactly what everybody else is doing, you just call it diffirently.

I don’t know why HDS keeps mentioning this thing as their advantage, this is nonsense comparing to other real advantages they have.

The number of hosts that can be attached is another story, but personally I’ve never seen more than, say, 30 servers attached to one storage box. Even if we multiply this by 2 for multipathing, this is still way below the limitation of most products on the market. So this is rather theoretical advantage.

I always find your posts very enlightning and very insightful.

You mention in your post that 1024 initiators can connect to a Physical Target port. To me that says that each Physical Storage Port has a queue depth of 1024. Assuming a reasonable LUN Queue Depth (32), you can not have more than 32 outstanding I/Os per LUN on that port, and more than 32 LUNs for ANY host type without being in danger of overrruning the target queue depth.

Of course you can connect 1024 initiators but with what host queue depth? 1?

Regards