V-Series and LUN 0

[ianaforbes]

Does anyone have experience with v-series appliances (not vfilers)? Chapter 6 in the planning guide states, 'Do not map LUN 0 to V-Series systems, even if LUN 0 is a storage LUN'. I just wanted to know why we're not supposed to map LUN 0 to the v-series? The guide doesn't go into any detail on this. I ask because I've already mapped LUN 0 and would like to know if something will break if I don't change things.

Cheers

Ian

[dandillharsch]

In our implementation it just didn't show up as a LUN that we could use.  Though I think there were other oddities with it but I can't recall at this point.

I would echo the doc though, don't use LUN0 when presenting storage to the vseries...

[rkaramchedu1]

LUN 0 is used by different array vendors for different things. EMC uses LUN 0 as a standard gatekeeper LUN. EMC CLARiiONs use LUN 0 as a virtual lun to check host connectivity, check zoning etc. This LUN may disappear after the checks are finished. If I remember right, Hitachi uses LUN 0 for special boot access. When a V-Series expects a LUN, it expects a LUN to overwrite and use for WAFL operations, so this may be the reason why they say not to use LUN 0...

my $0.02

cheers

[wilsonp]

Yes - that's all absolutely correct. Lun0 has special significance to many arrays - so best practice is to avoid using lun id 0.

[slusnia]

LUN0 was used by arrays and often presented as an unsupported size to V-Series.  This LUN is often <1GB which is less than what we support.  On IBM arrays, LUN31 was often an issue for the same reason.  We are building in fixes to future releases of ONTAP.

[MRJORDANG]

I have a similar question with ONTAP 8.1.1.   We are currently running ONTAP 8.1.1 on a v3240 HA pair.   We are using 3rd party virtualization and someobody mapped a LUN with ID 0 from the EMC Clariion to the NetApp v3240.   The v3240 see's the LUN fine and we are currently using it in an aggregate.

We are in the process of reconfiguring the 3rd party array and would like to "unpresent" all 3rd party array LUN's.   Seeing this note about LUN 0 makes me wary of unpresenting LUN 0 from the EMC array to the NetApp.    Can I remove simply remove LUN 0 using the process outlined in the vSeries Maintenance guide or do I need to handle LUN 0 in a special manner?

Thanks,

-J

[slusnia]

Starting in Data ONTAP 8.1, you can map LUN 0 to Data ONTAP if it is a storage type LUN.

[MRJORDANG]

Thank you for the response slusnia.  It seems to have mapped fine and we had no issues using it.  We would like to unmap it now.  

Does this mean, as of ONTAP 8.1, that I can also unmap our 3rd party array (Clariion) based LUN0 from the v3240 without downtime/issues?

[billshaffer]

For what it's worth, we had lun0 mapped and used for years in my old environment with no issues (set up this way by the PS guys, and by the time I saw the note not to use lun 0 it was too late).  This was a V3020 running various versions of ontap 6, 7 and 8.0 against HDS USP-V.  It also worked on a V3240 with ontap  8.0 against HDS VSP.  Never saw a problem.

Bill

[MRJORDANG]

I really appreciate the feedback!

We are also having no problems using LUN0 on our v3240.   We are just looking to unmap our Clariion based LUN0 from the v3240 and I see various notes in NetApp documents regarding special handling of LUN0 from 3rd party arrays.

Sounds like you had no problems.   Does that mean you also had no problems unmapping a 3rd party LUN with a host id of LUN0 from your v3020/v3240?

[billshaffer]

Hmmm, I don't think I ever tried!  As I recall, lun0 was used for aggr0/vol0, so pulling it was never really something I would have wanted.  I wouldn't think there would be an issue, but then then as you say the docs do have warnings.  Might be worth talking to support about.

Bill

[MRJORDANG]

I see.  Our aggr0/vl0 is on a NetApp shelf.   The Clariion LUN's were just hosting user data.  

I currently have ticket open with support.  The person I am working with doesnt seem to know either.   He is running it by some more senior engineers.  Just waiting for him to respond now.

It sounds like slusnia said we can map LUN0 as of ONTAP 8.1.  I am assuming this means we can unmap it as well.   Sounds like 8.1.x handles 3rd party LUNs mapped as LUN0 a little better.  I am trying to confirm this with support but still waiting to hear back.

[aborzenkov]

The problem is, as soon as you unmap real LUN 0 it is replaced by pseudo LUNZ. Having LUN 0 is a must for SCSI. Now how will NetApp react to LUN that suddenly changed all its properties?

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17.01.2013, в 20:40, "billshaffer" <xdl-communities@communities.netapp.com<mailto:xdl-communities@communities.netapp.com>> написал(а):

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Re: V-Series and LUN 0

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For what it's worth, we had lun0 mapped and used for years in my old environment with no issues (set up this way by the PS guys, and by the time I saw the note not to use lun 0 it was too late). This was a V3020 running various versions of ontap 6, 7 and 8.0 against HDS USP-V. It also worked on a V3240 with ontap 8.0 against HDS VSP. Never saw a problem.

Bill

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[billshaffer]

aborzenkov:

Not sure about that.  If lun0 were absolutely needed, would the docs say not to use it?  Seems that I've seen lunids starting at 1 on several different systems with no issues.

Bill

[MRJORDANG]

A quick update.   I was able to remove all of the LUNs, including LUN 0, from the NetApp v3240 without any issues.  I spoke with support who had to bounce it off of the more senior engineers.  Even then it was difficult to get a straight answer but they eventually assured me that it would be safe. I also bounced it off of a NetApp Professional Services Consultant and he said mapping LUN 0 from a 3rd party array to a v3240 is typically not a problem with EMC storage devices.   We were using a EMC CX4-480 Clariion.

So, I can say it worked without issue with ONTAP 8.1.1 on a v3240 with a number of LUNs (inlcuding LUN 0) being presented from an EMC Clariion CX4-480.

Here are the instructions that were provided:

1.  offline the aggregate containing the LUNs from the 3rd party array.

2.  Destroy the aggregate containing the LUNS from the 3rd party array.

3.  ON the v3240, perform a disk remove -w <diskName> on each of the disks (luns) presented from the 3rd party array.  This will result in the disks (luns) becoming unowned.

4.  On the Clariion, unmap the LUNs from the v3240.  We did this from Unisphere (an EMC array management product).  We chose to unmap the LUNs one at a time just to be safe.

This resulted in no panic or filer issues, including when we unmapped LUN 0.

I hope this helps somebody in a similar situation.