XenServer Question

Zaits

Hello Everyone,

I have a couple design questions I was hoping someone would be able to help with.

-I've configured 2 blades with XenServer 5.6 and added them to a resource pool. I need to add a storage repository now and was wondering should I add storage to each server or to the pool that will hold my VM's. Since I want to use XenMotion does my storage need to be attached to the pool? Also I know Vmware can migrate the datastore as well as the virtual machine, can XenServer do this as well?

-It appears Thin Provisioning is only configurable via CLI and this question kind of ties into my first one. I was able to configure a SR for a single server that had Thin Provisioning enabled except I was not able to get the SR to attach to the pool with Thin Provisioning enabled.

Thanks,

MentholMoose

Zaits wrote: »

Since I want to use XenMotion does my storage need to be attached to the pool?

Yes, both hosts will need to be connected to the storage. If the hosts are configured in a pool and you add the storage via XenCenter, it should connect to both hosts automatically. If you use the CLI you have to add it to each host manually, or as a shortcut you may be able to add it to one host and use the repair option in XenCenter for the other hosts.

Zaits wrote: »

Also I know Vmware can migrate the datastore as well as the virtual machine, can XenServer do this as well?

No it cannot.

Zaits wrote: »

-It appears Thin Provisioning is only configurable via CLI and this question kind of ties into my first one. I was able to configure a SR for a single server that had Thin Provisioning enabled except I was not able to get the SR to attach to the pool with Thin Provisioning enabled.

There may be some other problem. Can you confirm that the second host definitely has access to the storage?

Zaits

MentholMoose wrote: »

Yes, both hosts will need to be connected to the storage. If the hosts are configured in a pool and you add the storage via XenCenter, it should connect to both hosts automatically. If you use the CLI you have to add it to each host manually, or as a shortcut you may be able to add it to one host and use the repair option in XenCenter for the other hosts.

No it cannot.

There may be some other problem. Can you confirm that the second host definitely has access to the storage?

Thanks MenthoMoose for the quick response.

I definitely think I missed something with the configuration when I did it from the command line. It took me forever to get the right SCSI Device ID. I was issuing the command to create the SR and it kept failing saying the SCSI Device didn't exsist, but I was looking right at it and confirmed it with a fdisk -l.

Starke

What SAN are you running? You are much better off running thin provisioning on the SAN if it supports it. You should create the pool first with both of your hosts added then add your SR. Citrix XenServer DOES have something similar to Storage Motion, you just can't run it online. When the VM is turned off you can select Move VM and select your new SR. MM or I can probably answer any of your other questions, thanks.

Zaits

Starke wrote: »

What SAN are you running? You are much better off running thin provisioning on the SAN if it supports it. You should create the pool first with both of your hosts added then add your SR. Citrix XenServer DOES have something similar to Storage Motion, you just can't run it online. When the VM is turned off you can select Move VM and select your new SR. MM or I can probably answer any of your other questions, thanks.

Right now for testing we are using a Clariion AX-4 and soon we'll be upgrading to an more enterprise netapp equipment.

MentholMoose

Starke wrote: »

Citrix XenServer DOES have something similar to Storage Motion, you just can't run it online. When the VM is turned off you can select Move VM and select your new SR.

I have to disagree with this, for three reasons. First, the main characteristic of Storage VMotion is the fact that is can be done live, and XenServer lacks this functionality. Second, Storage VMotion is an actual move, and XenServer has no move functionality. There is Copy VM in XenCenter, or xe vdi-copy at the CLI, both of which are copy rather than move processes. That may sound like nitpicking, but it brings me to point three, Storage VMotion is highly automated, literally just a few clicks and you are done, and there is nothing similar included with XenServer.

Moving VMs in XS is a mess, not at all similar to Storage VMotion. Any scenario requires downtime, and with a large VM it can take many hours. With Copy VM in XC you end up with a VM that is not even identical to the original, so when you're done you have to edit it to fix settings that changed, such as the MAC address (assuming you care). Then you verify the copied VM works, and manually delete the original VM and disks. Alternatively you can detach the drives from both the original and the copy, attach the copied drives to the original, verify the original VM works, then manually delete the copied VM and original disks.

Alternatively you can use xe vdi-copy to copy the disks to the new location. When that's done, you can detach the disks from the original VM and attach the new disks, verify the VM works, and finally delete the original disks. This is probably scriptable, but that is a hassle (I've scripted the vdi-copy portion only). Also there is no progress meter, so it's up to your imagination to determine when it might finish.

Also, if you are using XC, don't exit out of XC (to reboot, etc.) or else Copy VM will fail and you have to start over. And yet another potential problem is that XenServer assigns the vdi-copy to a random host in the pool, and it doesn't check if that host is available, so either method will have random failures if a host in a pool is unavailable (rebooting, being patched, whatever).

Sorry for the rant, I had to move a bunch of XenServer VMs recently and it was traumatizing.

Starke

I am going to have to disagree with you as well. Storage Motion is the ability to move a VM between datastores. In VMware you can utilize this feature while the VM is turned off if you do not have the proper licensing. Citrix XenServer has BOTH a Copy and Move VM option. I've attached a screenshot to show you this. Take a look at the section under Enhanced XenCenter in the What's New article. You may not be aware of it because it's a new feature of 5.6, you also only need to upgrade XenCenter. I have in fact used it in a 5.5 environment with XenCenter 5.6. Not trying to argue just to argue, I just don't want to spread misinformation. Thanks.

XenServer 5.6 - A Conversation on What's New ocb - Citrix Community

Flickr: JRedmond7's Photostream

MentholMoose wrote: »

I have to disagree with this, for three reasons. First, the main characteristic of Storage VMotion is the fact that is can be done live, and XenServer lacks this functionality. Second, Storage VMotion is an actual move, and XenServer has no move functionality. There is Copy VM in XenCenter, or xe vdi-copy at the CLI, both of which are copy rather than move processes. That may sound like nitpicking, but it brings me to point three, Storage VMotion is highly automated, literally just a few clicks and you are done, and there is nothing similar included with XenServer.

Moving VMs in XS is a mess, not at all similar to Storage VMotion. Any scenario requires downtime, and with a large VM it can take many hours. With Copy VM in XC you end up with a VM that is not even identical to the original, so when you're done you have to edit it to fix settings that changed, such as the MAC address (assuming you care). Then you verify the copied VM works, and manually delete the original VM and disks. Alternatively you can detach the drives from both the original and the copy, attach the copied drives to the original, verify the original VM works, then manually delete the copied VM and original disks.

Alternatively you can use xe vdi-copy to copy the disks to the new location. When that's done, you can detach the disks from the original VM and attach the new disks, verify the VM works, and finally delete the original disks. This is probably scriptable, but that is a hassle (I've scripted the vdi-copy portion only). Also there is no progress meter, so it's up to your imagination to determine when it might finish.

Also, if you are using XC, don't exit out of XC (to reboot, etc.) or else Copy VM will fail and you have to start over. And yet another potential problem is that XenServer assigns the vdi-copy to a random host in the pool, and it doesn't check if that host is available, so either method will have random failures if a host in a pool is unavailable (rebooting, being patched, whatever).

Sorry for the rant, I had to move a bunch of XenServer VMs recently and it was traumatizing.

astorrs

Starke wrote: »

I am going to have to disagree with you as well. Storage Motion is the ability to move a VM between datastores. In VMware you can utilize this feature while the VM is turned off if you do not have the proper licensing.

Sorry but I'm with Menthol on this one. You can only use Storage VMotion when a virtual machine is powered up otherwise you're just moving the VM files between datastores (what I could do with a simple mv at the ESX command line). It's nice to hear that Citrix has finally added the mv command to XenServer with v5.6

VMware wrote:

VMware Storage VMotion enables live migration for running virtual machine disk files from one storage location to another with no downtime or service disruption.

MentholMoose

Yes, XS is improving. I did not know about the new Move VM added in XS 5.6 two weeks ago. It's a welcome addition and more convenient than previous methods. I will have to try it out, though I don't think the other issues I mentioned have been addressed.

Zaits

Thanks guys for some really good material. I'm very new to XenServer and have a little experience with VMware so it's good to know what each product is capable of.