Which hosts belong in what pool when running local storage?
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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.
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@Pete-S said in Which hosts belong in what pool when running local storage?:
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.
Are you still able to live migrate a machine from one server to another?
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@dafyre said in Which hosts belong in what pool when running local storage?:
@Pete-S said in Which hosts belong in what pool when running local storage?:
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.
Are you still able to live migrate a machine from one server to another?
Yes, it works fine. It's shared nothing live migration. Take a while to do it since both local storage and memory is migrated.
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@Pete-S said in Which hosts belong in what pool when running local storage?:
@dafyre said in Which hosts belong in what pool when running local storage?:
@Pete-S said in Which hosts belong in what pool when running local storage?:
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.
Are you still able to live migrate a machine from one server to another?
Yes, it works fine. It's shared nothing live migration. Take a while to do it since both local storage and memory is migrated.
Right. But it is good to know that you are able to do that if needed... such as planned maintenance on one of the hosts.
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@dafyre said in Which hosts belong in what pool when running local storage?:
@Pete-S said in Which hosts belong in what pool when running local storage?:
@dafyre said in Which hosts belong in what pool when running local storage?:
@Pete-S said in Which hosts belong in what pool when running local storage?:
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.
Are you still able to live migrate a machine from one server to another?
Yes, it works fine. It's shared nothing live migration. Take a while to do it since both local storage and memory is migrated.
Right. But it is good to know that you are able to do that if needed... such as planned maintenance on one of the hosts.
True! And with 10GbE and SSD storage it's not too bad.
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Pooling the resources doesn't mean you need HC or even HA.
Pooling just says, if this host goes down some other hosts is ready to take the workload. You shouldn't be experiencing any issues like what you've described from using pooling.
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@DustinB3403 said in Which hosts belong in what pool when running local storage?:
Pooling the resources doesn't mean you need HC or even HA.
Pooling just says, if this host goes down some other hosts is ready to take the workload. You shouldn't be experiencing any issues like what you've described from using pooling.
You are right and you are wrong.
A pool is just a pool of hosts as you said but you actually need HA for another host to take the workload automatically. You could do it manually but in either case, the VMs storage or a copy of it needs to be accessible for the new host. So you need some kind of "shared storage" solution (SAN/distributed FS/replicated backups/whatever) to "move" a VM from a failed host.
With xenserver the pool is administrated through the pool master. If the pool master dies another host takes the master role - if you have HA enabled. If you don't have HA the entire pool will become unreachable. It's not fun.
https://docs.citrix.com/en-us/xenserver/current-release/hosts-pools.htmlThere are other issues as well, like when moving a standalone host to a pool all VMs on local storage will be erased.
All in all, unless you have some kind of shared storage solution/replication going on, it's less restrictive to have standalone hosts. At least with xenserver. You can still manage them centrally and move VMs between them as you please.
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So to answer my own question:
"Which hosts belong in what pool when running local storage?"The answer is none - at least with xenserver. Don't use pools when using local storage.
