[OmniOS-discuss] Ang: Re: Illumos/omnios ALUA support was:: Active-Active vSphere

Sun Nov 30 06:02:47 UTC 2014

Hi, Aron and others interested in this!

Thanks for your respons, and don´t worry about it length, since it is interesting.

I'll continue further down...

-----Aaron Curry <asc1111 at gmail.com> skrev: -----
Till: Johan Kragsterman <johan.kragsterman at capvert.se>
Från: Aaron Curry <asc1111 at gmail.com>
Datum: 2014-11-29 20:59
Kopia: Saso Kiselkov <skiselkov.ml at gmail.com>, "omnios-discuss at lists.omniti.com" <omnios-discuss at lists.omniti.com>
Ärende: Re: [OmniOS-discuss] Illumos/omnios ALUA support was:: Active-Active vSphere

Johan,

It looks to me like your understanding of ALUA is correct.

Bottom line: ALUA is a way to present a LUN to a host while advertising all possible paths. These "possible paths" include the local target HBAs as well as any other target HBAs in the ALUA group. This is necessary in a high availability storage solution!

What I would like to know here, is which software is responsible for advertising the LUN(-s) as prefered  or not prefered? Would that be the stmf proxy service?

With all that said, while I don't think that getting ALUA up and running is that complicated (assuming you can get enough information to help you out with the process) the problem is, where do you go from there? Highly available storage is only good if a secondary node can take over when the primary node fails. How do you manage that? How do the nodes in a cluster monitor each other? How does a secondary node import a pool and change the configured LUNs from standby to active (changing from standby to active is not actually handled by ALUA)? And then what do you do when the primary comes back online? How do you keep it from trying to take over? How do you avoid split-brain scenarios? This is where the cluster management software comes into play, and where things get really complicated. There are lots of moving parts here to try to manage and coordinate. You can try to write up all the scripts yourself. I have seen references to a set of open source utilities that people have used with varying degrees of success.

Saso has a cluster solution here, that I still haven't tried, but I know other has:

http://zfs-create.blogspot.se/2014/05/building-zfs-storage-appliance-part-2.html

That is one of the reasons I went in to this discussion, that I wanted to be able to understand how to get ALUA into that solution.

Saso, do you got any software for your stmf-ha that is comparable to the RFS-1 stmf proxy service?

I saw this "Feature #3775 Upstreaming of ALUA use-after-free fixes from Nexenta", is that something that is usable for your solution?

If so, got any docs for how to implement that?

Sorry for this being so long. If you're still reading at this point... wow, you must be really interested in this topic. For those who have made it this far, the bottom line to the ALUA question is this: ALUA is only needed in an HA setup. And, if you need HA and want to use OmniOS, then you're much better off buying a license for RSF-1.

I agree about buying an RFS-1 license for important production clusters, but there are many other scenarious where you would like to have access to this: In education, in your own process of understanding how things work, for small companies that don't have the money yet, but want to give it a shot, etc.

 For me, I'd like to set it up and get it running to get a good understanding how it all works. I want to understand the software, I want to undestand the processes.

Regards Johan

Aaron

On Sat, Nov 29, 2014 at 2:10 AM, Johan Kragsterman <johan.kragsterman at capvert.se> wrote:
So, since this subject seams very much to be around ALUA understanding, this might be a good opportunity to discuss Illumos/OmniOS ALUA implementation..?

So I change/alter the subject, if you folks don't mind...?

If you mind, I can start a new thread...?

I continue further down...

-----"OmniOS-discuss" <omnios-discuss-bounces at lists.omniti.com> skrev: -----
Till: Rune Tipsmark <rt at steait.net>
Från: Saso Kiselkov
Sänt av: "OmniOS-discuss"
Datum: 2014-11-28 15:54
Kopia: "omnios-discuss at lists.omniti.com" <omnios-discuss at lists.omniti.com>
Ärende: Re: [OmniOS-discuss] Active-Active vSphere

On 11/28/14 3:34 PM, Rune Tipsmark wrote:
> Okay, i noticed alua support is not enabled per default on omnios. How do i enable that?

The process is complicated, not very well documented and it isn't meant
for your scenario anyway. If you only have one storage node, then you
don't need ALUA, even if you have multiple connections to the node. So
no need to worry about it.

When you say it is poorly documented, I suppose you mean ALUA on Illumos dists?

If you mean on Illumos dists, I haven't found any documentation, apart from your(Saso) patch Feature #3775. If you know of any such documentation, pls give us a link to it.

There are some documentation though, from Nexenta and high-availability.com, but I find this difficult to use in OmniOS, since it's only Nexenta focus(of coarse).

One thing I don't understand is if the Nexenta implementation of ALUA use access through the "not prefered path" to the LUN(-s), even through the node that doesn't own it?? In my understanding, that would need a complicated interconnect between the head nodes, as well as a LU pass-through handling through the "not prefered path-node", wouldn't it? And I haven't seen that anywhere in Illumos/Nexenta, but of coarse, I might be wrong here...?

If I'm right here, the Nexenta implementation of ALUA is not providing the connection to the LUN(-s) through the "not prefered path", it only provides access after failover, when the "not prefered path" has become the "prefered path"?

If I'm wrong here, and have failed to understand something, pls enlighten me...

I'm also curious about the NMC, Nexenta Management Console. Is that one also in illumos-gate, or any equivalent software...?

If not, we would need to add and check the target group members on both(all) nodes manually, right?

How is this related to your implementation of stmf-ha, Saso?

Regards Johan

Cheers,
--
Saso

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