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Hypervisor -> migrating from from local storage + stand-alone servers to shared storage in a cluster - What is the best approach?


Carlo Piva1709156772

Question

When we first started working with XenServer back with 6.0, I had suggested initially that we configure everything into a cluster using shared storage right off the hop, for fear of this very scenario. Of course, my manager had heard from another person that we could use local storage so that meant we could roll things out getting additional server hardware,  and not have to worry about making room on our existing SAN or purchasing a new SAN for that project. That was about 5 or 6 years ago now. There are currently 2 servers that are live. I have tried my best to keep the servers up to date, but as each has live data, isn't being backed up, and has no access to shared storage, this has been a bit of an ordeal. Currently, the XenServers are at 7.1 CU2 in terms of patch level. 

 

Now some additional server equipment has been freed up (2 repurposed dell servers), and I was asked to install the latest and greatest version of XenServer (Hypervisor 8.1) and setup the  machines as a cluster with high availability enabled. It was also suggested that I should use GFS2 to take advantage of thin provisioning and performance increases. A new san has been placed at our data center with a lun configured for shared storage for XenServer.

 

I know by default, one can not simply move a VM from LVM to GFS2, so I created a small VM which would allow me to export from one server and re-import to another server locally at the data center. 

Its slow, not elegant, but it works, so moving the VM's over isn't the issue.

 

The issue I am facing is just trying to figure out the best possible path to achieve our goals

My manager did not like the idea of starting off at 7.1, setting up the SAN environment, and then joining the existing hosts to the san.

His prefered method was to go straight to 8.1 on one of the 2 "new" (not new, just repurposed) servers setup the san, pool, cluster, and HA. Migrate the VM's from one host to the new pool but leaving the originals unscathed on the original host. Then, when we are ready, turn the migrated VM's online, shutdown the old server, convert it to Hypervisor 8.1, then join it to the pool.

My initial attempts with the two "new" servers, was to install Hypervisor 8.1 on both, setup the networking on both, create a pool on one, join the other to the pool, set up multipathing, then connect the san. There was an issue where one host refused to connect to the san (Funny, it was the pool master), and Multipathing kept disabling and re-enabling itself. After talking with Citrix, they asked me to reinstall Hypervisor 8.1 on that server. So I did after making the other host the new pool master.  However, after reinstalling Hypervisor, it will no longer join the existing pool. Throws an error that indicates that there multiple IP's configured, even when the only one configured is the management IP, and no it's not in a bond.

 

25 hours in to trying to fix this problem and various others, several hours on the phone with citrix support,  and its becoming clear that this method isn't going to work - at least i"m not seeing a solution readily available. 

 

When I first started this, my thought process was to install Citrix 7.1 CU2 on the "NEW" servers. create a pool, setup the san, join all the hosts to the pool, and perform pool upgrades to get all the servers to a high enough patch level. Then configure the SAN (as GFS2 with multipathing enabled), migrate data off the hosts to the SAN (using my vm), and once that is done, upgrade one server at a time to Hypervisor 8.1. I'm not positive if this is any better than what I have been doing. In writing this out I can see some possible gotcha's (mainly dealing with version levels being different the moment one host is upgraded to 8.1 as it will no longer function as part of the pool until the others are brought up to the same level).

 

A new thought I have is the same as the above, but leave out GFS2 and multipathing, just format the lun as LVM so that migration would be smoother albeit not optimal, then create a seperate HR with a new LUN with the same amount of dedicated space, and have that one configured for GFS2. This means I would have to migrate the data a second time, from LVM to GFS2.  before purging the old settings and LUN. 

 

Does anyone have a suggestion as to the best approach for this? I've been searching for a good migration path approach for close to a week now, and I feel like i'm taking more steps back than I am going forward.

 

 

Carlo

 

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XenServer at times can be a real bear. I don't know on 8.1 as I am still 7.1 version. I would probably do what you are thinking 

and install 7.1 on those two newly provisioned servers and either migration live or export/import your data over to the new

ones.   Are you running free or licensed ? I would just stay 7.1 LTSR for a while if you can. AS far as GFS2 I wouldn't go that

route until it becomes a little more mainstream. 

 

--Alan--

 

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Not sure once the VMs along with their storage are on the new 8.1 pool why the VDIs cannot be just migrated to other SRs for starters. I do not see a big advantage currently with GFS2, either, other than you nee some huge storage options. I'm not sure storage migration even works on GFS2 in particular if a VDI is larger than 2 TB.

 

With enough resource on a new 8.1 pool I would live migrate the VMs over of possible and spare yourself potential inconsistencies upgrading from 7.1 to 8.1 o the new pool.

Back up all VMs first, of course. If a storage migration fails it generally leaves things intact on the source host and storage. But you do not want to risk this -- I had a bad experience there once when storage migrating a few VMs from 6.5 SP1 to 7.1.

 

-=Tobias

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Hi Tobias and Alan.

After several hours of troubleshooting and reinstalling Hypervisor 8.1 on both hosts, and doing my own research. As Alan stated GFS2 is not really mainstream right now. I have found some sites that suggest that GFS2 is actually a stable beta, and not fully implemented at this time as a lot of needed features are currently missing. Stability was also something that seemed to be in question. So based with this information, I explained we are better using LVM for the time being and can revisit GFS2 at a later date. My manager was going by recommendations for GFS2 as per Citrix recommendation off their website touting it as more efficient, less SAN overhead, and reduced file sizes. It wasn't until I had these issues and looked deeper into it that I saw many people experiencing problems with its current implementation. 

 

This problem is done, on to the next (which I already posted because this project is driving me nuckingfutz)

 

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