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HPUX 11.x and EMC Symmetrix LUN address limitation

Aaron Newcomb
Occasional Contributor

HPUX 11.x and EMC Symmetrix LUN address limitation

Has anyone successfully been able to see a LUN from an EMC Symmetrix that is assigned at 08 through 0F? There seems to be a serious limitation on the part of HP to be able to see all 256 possible LUN addresses from a single fibre channel initiator. I can only see devices that are addressed in the 0 - 7 range (i.e. cXt0d7 but not cXt0d8). I thought that patch PHKL_25118 was supposed to fix this, but so far I cannot get it to work. Also, what is the stated upper limit of the number of devices that HPUX will recognize on a single HBA (A5158A in this case) given that it could connect to multiple subsystem ports through a switch?
11 REPLIES
harry d brown jr
Honored Contributor

Re: HPUX 11.x and EMC Symmetrix LUN address limitation

Deshpande Prashant
Honored Contributor

Re: HPUX 11.x and EMC Symmetrix LUN address limitation

Hi
On my system I see luns through cXtYd0 through cXtYd7.
I remember, EMC Eng. mentioning me on HP fiber adaptors the performance degrades after 128 LUNs and so we converted them to Meta-volumes.

Thanks.
Prashant.
Take it as it comes.
Aaron Newcomb
Occasional Contributor

Re: HPUX 11.x and EMC Symmetrix LUN address limitation

Harry,

Thanks for the info. The patch you reference was re-released to resolve issues with PHKL_25118, but does not include the LUN address fix. We are not having problems with the PHKL_25118 patch so I don't think going backwards would resolve the situation.

Prashant,

I would re-visit that issue with EMC if I were you. The number of LUNs alone should have no bearing on performance unless your data suggests that throughput would be an issue. I could have thousands of LUNs (theoretically) on an HBA and as long as only one LUN was being accessed at a time I would never run into performance problems. It all depends on your particular setup.
Aaron Tatone
Frequent Advisor

Re: HPUX 11.x and EMC Symmetrix LUN address limitation

Aaron,

You are correct. All HP-UX hosts can only have 7 Disks (luns) per Target. That is because the Controller is an 8-bit (1 byte)field (00-FF), the Target is a one-byte field (00-FF) and the Disk is a 3-bit field (00-08). I have called HP and talked to their back line about this. The only way to get sixteen LUNS per target is to be running a superdome with HP-UX 11i and all the appropriate patches.

Hope this helps

Aaron
Aaron Tatone
Frequent Advisor

Re: HPUX 11.x and EMC Symmetrix LUN address limitation

As a side note, this same issue (only 8 LUNS) occurs for all storage devices attached to HP servers, including the HP storage (VA7x00, XP, etc).

Aaron
Vincent Fleming
Honored Contributor

Re: HPUX 11.x and EMC Symmetrix LUN address limitation

I beg to differ, Aaron.

What actually happens is that the actual LUNs are mapped to "ghost" targets in FC. If there are 32 LUNs, 4 ghost targets are created... You certainly can "see" all of the LUNs on the SAN.
No matter where you go, there you are.
Aaron Tatone
Frequent Advisor

Re: HPUX 11.x and EMC Symmetrix LUN address limitation

you're right. You see all LUNs, but after the eighth disk, the t# increments.

i.e.
c0t0d1 - LUN 1
c0t0d2 - LUN 2
c0t0d3 - LUN 3
c0t0d3 - LUN 4
c0t0d4 - LUN 5
c0t0d5 - LUN 6
c0t0d6 - LUN 7
c0t0d7 - LUN 8
c0t1d0 - LUN 9
c0t1d1 - LUN 10

Re: HPUX 11.x and EMC Symmetrix LUN address limitation

I agree with Aaron,
With hp you can only have a total of 8 luns per target. HP-UX simply does not scan the bud above those luns...


Liam
Stuart Abramson_2
Honored Contributor

Re: HPUX 11.x and EMC Symmetrix LUN address limitation

1. There is a very good short white paper on the hpux web sited called

Maximum LUN configuration considerations for HP-UX.
www.docs.hp.com

2. The limits are:

cCtTdD:
cC:
tT: 0-15
dD: 0-7

15 x 7 = 105 PVs on a single "vbus"

3. But you can have multiple "vbus"-es.

vbus might be an EMC term.

When the vbus changes, the C number increments.

4. The limit is 256 PVs/HBA (I think!).

It turns out that is both an HP and an EMC limit (I think).
Aaron Newcomb_1
Occasional Visitor

Re: HPUX 11.x and EMC Symmetrix LUN address limitation

Actually, if you check your math you will find that for a single vbus you can address 8 devices x 16 targets (don't forget to count 0) = 128. There are 8 vbus's ( 0 - 7 ) so that means it is technically feasible to get 1024 devices on a single HBA. However, EMC recommends not putting more than 256 devices per symmetrix port. Other vendors probably have their own recommendation so it is best to check before you run into a non-supported setup.

Re: HPUX 11.x and EMC Symmetrix LUN address limitation

doh! but of course....