Which hosts belong in what pool when running local storage?
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Are there any consensus on what VM hosts belong in the same pool when all hosts are running on local storage?
I'm using xenserver (xcp-ng).
I have two distinct usage for the hosts, one is for development and benchmarking and the other is for production.
There is no HA at the hypervisor level. VMs either have failover at the application level using load balancers/proxies or don't require HA at all.
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@Pete-S said in Which hosts belong in what pool when running local storage?:
I'm using xenserver (xcp-ng).
Are you using XenServer or XCP-ng (they are different products).
A individual host can be in it's own pool (and really should be if you only have 1 host). But if you have multiple hosts, create a pool and add all of your hosts to it.
If any host in that pool goes offline the VMs will be moved to the other working host in the same pool.
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And the simple approach that I have taken (in my lab and production) is all host that have the same generation & family of CPU get added to the pool.
Anything outside of that isn't added, because it could cause issues.
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The biggest issues that can occur with different gen CPUs across hosts is that, generally your VM would need to reboot to reconfigure the hardware.
Not an ideal approach if you need 100% uptime. But neither is not having HA if you require HA.
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@DustinB3403
Just to clarify, I'm running xcp-ng. And no HA at the hypervisor level so if a host dies all VMs will die with it.I have some machines that will run on bare metal or containers but about 12-14 hosts will be running xcp-ng. Some are 1 CPU and some are 2 CPU but they are the same generation.
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@Pete-S said in Which hosts belong in what pool when running local storage?:
@DustinB3403
Just to clarify, I'm running xcp-ng. And no HA at the hypervisor level so if a host dies all VMs will die with it.I have some machines that will run on bare metal or containers but about 12-14 hosts will be running xcp-ng. Some are 1 CPU and some are 2 CPU but they are the same generation.
So create 1 large pool, add all of your hosts to it. This will allow your VM's to migrate (or be evacuated) from 1 hosts to any other host in the pool.
Assuming that the other hosts have enough resources (space and RAM) to host the new guests.
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I'm assuming all of these hosts are within the same LAN and not crossing any large geographic distances.
Which if they are separated like that. I would create geographic pools for the hosts within those datacenters.
This doesn't prevent you from manually sending a VM to a different pool. It just ensures that your guests aren't traversing the internet during a migration "because there were resources there".
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@DustinB3403 said in Which hosts belong in what pool when running local storage?:
I'm assuming all of these hosts are within the same LAN and not crossing any large geographic distances.
Which if they are separated like that. I would create geographic pools for the hosts within those datacenters.
This doesn't prevent you from manually sending a VM to a different pool. It just ensures that your guests aren't traversing the internet during a migration "because there were resources there".
Yes, it's the same location, actually the same rack.
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@Pete-S said in Which hosts belong in what pool when running local storage?:
Yes, it's the same location, actually the same rack.
So one pool with all 12-14 hosts would be perfectly fine. Even ideal (again assuming you're using XO to manage everything) as you can perform rolling pool upgrades.
Which allows your VMs to just move when needed and not ever have to be touched by hand.
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One pool would also allow any of your guest VMs from any host to move if an issue occurred on the fly.
"Oh server 3 is down" look at that, everything is still running on my other hosts in the pool.
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@DustinB3403 said in Which hosts belong in what pool when running local storage?:
One pool would also allow any of your guest VMs from any host to move if an issue occurred on the fly.
"Oh server 3 is down" look at that, everything is still running on my other hosts in the pool.
Makes sense. But maybe I should put production in one pool and development & benchmarking in another. Then I could test any updates on the development pool first. It's the same hardware.
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@DustinB3403 said in Which hosts belong in what pool when running local storage?:
Which allows your VMs to just move when needed and not ever have to be touched by hand.
I've never tried this, but do you need shared storage for this?
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@bnrstnr said in Which hosts belong in what pool when running local storage?:
@DustinB3403 said in Which hosts belong in what pool when running local storage?:
Even ideal (again assuming you're using XO to manage everything) as you can perform rolling pool upgrades.
I've never tried this, but do you need shared storage for this?
The approach is that nothing is shared. So it won't be HA. The VM will still have to migrate to that system. But that would occur via a snapshot and migrate.
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@Pete-S said in Which hosts belong in what pool when running local storage?:
@DustinB3403 said in Which hosts belong in what pool when running local storage?:
One pool would also allow any of your guest VMs from any host to move if an issue occurred on the fly.
"Oh server 3 is down" look at that, everything is still running on my other hosts in the pool.
Makes sense. But maybe I should put production in one pool and development & benchmarking in another. Then I could test any updates on the development pool first. It's the same hardware.
That would make sense if you have the resources. There is no harm or foul.
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@DustinB3403 said in Which hosts belong in what pool when running local storage?:
@bnrstnr said in Which hosts belong in what pool when running local storage?:
@DustinB3403 said in Which hosts belong in what pool when running local storage?:
Even ideal (again assuming you're using XO to manage everything) as you can perform rolling pool upgrades.
I've never tried this, but do you need shared storage for this?
The approach is that nothing is shared. So it won't be HA. The VM will still have to migrate to that system. But that would occur via a snapshot and migrate.
Ah OK, I have live migrated some smaller VMs, but I've never actually done the rolling pool upgrades because I have some pretty big VMs that it's so much faster just to shut down and restart during planned downtime.
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@bnrstnr said in Which hosts belong in what pool when running local storage?:
@DustinB3403 said in Which hosts belong in what pool when running local storage?:
@bnrstnr said in Which hosts belong in what pool when running local storage?:
@DustinB3403 said in Which hosts belong in what pool when running local storage?:
Even ideal (again assuming you're using XO to manage everything) as you can perform rolling pool upgrades.
I've never tried this, but do you need shared storage for this?
The approach is that nothing is shared. So it won't be HA. The VM will still have to migrate to that system. But that would occur via a snapshot and migrate.
Ah OK, I have live migrated some smaller VMs, but I've never actually done the rolling pool upgrades because I have some pretty big VMs that it's so much faster just to shut down and restart during planned downtime.
Yeah there are many benefits to having planned downtime. This is just a "nice to have if so required" type feature.
An alternative would be to use 2-3 hosts to create a separate Continuous Replication pool (assuming you could afford the lost capacity) and have all of the production works CR'd to that pool.
Then it would just be a matter of rapid cloning the VM and powering it on.
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@bnrstnr said in Which hosts belong in what pool when running local storage?:
@DustinB3403 said in Which hosts belong in what pool when running local storage?:
Which allows your VMs to just move when needed and not ever have to be touched by hand.
I've never tried this, but do you need shared storage for this?
Should not. It's like "Storage vMotion" when the storage is not shared.
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I'll just want to confirm that I will go with one pool for production and one pool for development and benchmarking.
Citrix recommendation for Xenserver is to have production & development hosts in separate pools and it makes sense just from avoiding avoiding human mistakes as well.
Also all the hosts in the pool share the same network config so it also makes sense to have development in it's own pool in case one want to test something out.
Ideally, I'd have one set of switches for each pool as well, but I'll have to settle for different vlans for now - for budgetary reasons.
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@Pete-S said in Which hosts belong in what pool when running local storage?:
I'll just want to confirm that I will go with one pool for production and one pool for development and benchmarking.
Citrix recommendation for Xenserver is to have production & development hosts in separate pools and it makes sense just from avoiding avoiding human mistakes as well.
Also all the hosts in the pool share the same network config so it also makes sense to have development in it's own pool in case one want to test something out.
Ideally, I'd have one set of switches for each pool as well, but I'll have to settle for different vlans for now - for budgetary reasons.
Sounds like a reasonable plan.
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Just wanted to provide an update.
I started as intended and put all hosts in two pools but I have changed it since. It simply doesn't work well if you aren't running shared storage and doing HA in the pool.
So now all hosts are individual hosts and don't belong to any pool. I found it to be the most flexible setup when you're not using shared storage.
