One ISCSI SAN, 2 ESXi Hosts, failover VMs?

Bookmage

Gawd
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Sep 2, 2004
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Since I'm a cheapskate? and trying figure to figure out the benefits of ESXi and figuring out how to reduce downtimes for a server. I had a thought about cutting downtime but I'm not sure if ESXi works the way I hope it does.
So here's the idea:

Have 1 ISSCI SAN to store all the VMs and related files Have 2 ESXi hosts on usb drives connected to it. Setup VM1 on Host1 pointing to VM files on SAN. Duplicate/import VM1 on Host2 pointing to the same VM files. Have VM1 running on Host1.
Assume VMs run some webapp or function as a real server w/all the real server consequences which I accept, ie power failure can cause dataloss, etc.

If I shut down VM1 on Host1, can I start VM1 on Host2 and have it work and function where it left off?
If I pull the plug on Host1 can I start VM1 on Host 2 and have it roughly pick up where it left off?

Has anyone tried this? or have a setup to quickly test this?
Or does anyone know enough about the workings of ESXi to explain what it does to the VM files? ie will the VM files on the SAN be corrupted because ESXi didn't "close" the VMs?

Thanks for the input!
 

NetJunkie

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Yes..you can boot a VM on either system, manually. If you want the VM to restart on the second ESXi host automatically you need to license them and gain VMware HA. Don't import a VM in to the second ESXi box until you're ready to boot it or you may really corrupt something.

Depends what you mean by "pickup where it left off.". It's a reboot..just like you pulled the power to a running physical server and then rebooted it. If you really want it to failover where it left off (active system) then you need to license them up and implement VMware FT (Fault Tolerance).
 

Bookmage

Gawd
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so I can't have the vm setup on both hosts and have one turned on and the other turned off? the Both vmhosts will actively read the status of hte vm files on the san
 

nitrobass24

[H]ard|DCer of the Month - December 2009
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Hyper-v will do that, otherwise you need to buy a license for ESX
 

MikeTrike

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Citrix XenServer does the same thing, auto failover requires a license. However if you are logged into XenCenter you can just drag it over to the other node. XenServer works as a cluster, each node contains the cluster data, so if one node goes down the other can take over control. Still you'd need to tell the VM's to boot up manually if you dont want the licensing that gives you HA. However the licenses are $1000MSRP, or about $850~ per node if you go with some place like CDW or Insight, etc. Also nicer because it's licensed per node in the sense that you can have as much RAM, CPU cores, CPU sockets you want and its the same price. Unlike VMware

older site, but valid info still:
http://xenserver5.com/whatsnew.php

Currently building out a FC SAN + 2 powerful AMD opteron nodes so this is all fresh in my head. What with all the phone calls with CDW/EMC/Citrix lately. :)
 

NetJunkie

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so I can't have the vm setup on both hosts and have one turned on and the other turned off? the Both vmhosts will actively read the status of hte vm files on the san

Since the two servers are not in a cluster they aren't talking.... They will both try to lock the config files. Might work..might not. Test it on a throwaway VM.
 

Bookmage

Gawd
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Thanks for the input, I'll have to look more into Hyper-V and see how far it's progressed. Haven't looked much into Xenserver so I'll have to add that to the list.

well it doesn't need to be automatic, I'm ok with having to autostart it, but i was wondering if I could just have the VMs "setup" on another esxi host or if i have to disassociate it from a vmhost in some fashion. I'll have to look into the hosts locking the VM file, hadn't thought about that, which is why i pose the question before spending time testing it out...

Similar scenario: one ESXI host hooked up to the ISCSI san. If the ESXI host fails, I should be able to load up esxi on another box and just import the VMS to it, right? And I would hope the VMs function like a server w/incomplete shutdown.

Yeah, these are just thoughts w/o any intensive googling or anything. I am curious as to how many shops are using which Visualization setup and they handle disaster recovery, ie vmhost goes down or something. I also need to figure out VMs get backed up or if i should just do a backup of the running server...
 

MikeTrike

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Similar scenario: one ESXI host hooked up to the ISCSI san. If the ESXI host fails, I should be able to load up esxi on another box and just import the VMS to it, right? And I would hope the VMs function like a server w/incomplete shutdown.

I think you can do that with vmware, as the database resides on it's own standalone system. (vsphere?)

XenServer is completely different, two nodes are needed for failover from the start (well this part isn't). Databases are clustered across your nodes, so self healing in a sense. Node dies and loses everything, no problem. Repair, re-install, re-join the cluster as a new node and it will get the info from the remaining nodes.

Yeah, these are just thoughts w/o any intensive googling or anything. I am curious as to how many shops are using which Visualization setup and they handle disaster recovery, ie vmhost goes down or something. I also need to figure out VMs get backed up or if i should just do a backup of the running server...

Definitely look into XenServer a bit more.
 

The_Mage18

[H]ard|Gawd
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Take a look at Suse Linux Enterprise Server and Red Hat Enterprise Linux. Both include XEN virtualization. Suse has HA functionality and migration capability without additional cost.

Citrix's offering is pricey when you start including support and add-on modules.
 

lopoetve

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Oct 11, 2001
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Yes..you can boot a VM on either system, manually. If you want the VM to restart on the second ESXi host automatically you need to license them and gain VMware HA. Don't import a VM in to the second ESXi box until you're ready to boot it or you may really corrupt something.

Depends what you mean by "pickup where it left off.". It's a reboot..just like you pulled the power to a running physical server and then rebooted it. If you really want it to failover where it left off (active system) then you need to license them up and implement VMware FT (Fault Tolerance).

The HB regions in VMFS will keep it from corrupting anything in the disks, but the config files may get a bit funky and out of sync.

It will do what you want though.
 

lopoetve

Fully [H]
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Oct 11, 2001
Messages
32,613
Since the two servers are not in a cluster they aren't talking.... They will both try to lock the config files. Might work..might not. Test it on a throwaway VM.

Won't lock them unless the VM is up and running. You'd have to add it to both hosts before booting it. :)
 

Bookmage

Gawd
Joined
Sep 2, 2004
Messages
673
Ok so that works as I was hoping.
That should work well for my home lab.

Thanks for all the input.

Now I just have to evaluate the pros/cons of runnign a MultiTB file server in a VM. I need to come up with cons for my manager...
 
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