Homogeneous pools, how similar do the CPUs need to be?
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Yet another VMware refugee here, trying to figure out the best way to move into XCP-NG.
I see that pools are ideally created with hosts that have very similar processors. I'm wondering how dissimilar they can be before it causes problems, especially if I don't much care about live migration. I would mainly want to be able to restore backups between servers, if needed, or use replication backups for DR.
My main server is a PowerEdge R630 with dual:
Intel Xeon E5-2609 v3 1.9GHz,15M Cache, 6.40GT/s QPI, No Turbo, No HT, 6C/6TI'm adding a PowerEdge R730XD server with single:
Intel Xeon E5-2620 v3 2.4GHz,15M Cache, 8.00GT/s QPI, Turbo, HT, 6C/12T 1866MHz
Planning to add a second E5-2620 to that system in the near future.Are those similar enough to put in the same pool without problems or will it reduce the CPU features on the R730 just because they are in a pool together?
I'm also planning to buy a refurbished server. Either an R630 or an R730. If I should strive for an exact match for CPU then I'll get an R630 and put those two into a pool. the R730 is actually my personal server and it has a ton of storage so I was thinking I might use it as a remote for backups.
For instance, I found an R630 with dualIntel Xeon E5-2699v4but I wonder if that's too different from the E5-2609 in my older one. I'm guessing the R640s I see with Xeon Gold CPUs are probably plenty different enough to cause issues but I just don't know.Thanks for helping me get up to speed on all this. Nothing like having to make major platform decisions when trying to also make a hardware purchase when I know I have to live with my decision for years to come.
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@CodeMercenary As stated in the docs, a pool can not be a mix of AMD and Intel, but you can have different Intel CPUs in the same pool. The pool will use the features of the lowest CPU. This does not affect Mhz, cores, turbo, or HT. Each machine can be a little different and be good. They will just use the common features available on both CPUs. I don't see a problem with the different E5 v3 CPUs. Adding in a E5 v4 CPU will be ok but not show additional features to the guests. You should have a consistent set of network interfaces as the pool will expect them to be the same type in the same order.
Take a look at the docs for pool requirements.
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@CodeMercenary Another thought is you could also upgrade the older v3 CPUs to v4 (at some time later). I've done this on an active pool without shutting down guest VMs.
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I've read through the pool requirements more than once but I was trying to understand how much I'd lose by mixing them. You've helped me understand that a bit better. Thank you.
I just wouldn't want to pay more for v4 CPUs in one of the systems if being in the same pool means I lose features I care about. I don't know that I'd care about features outside of the bigger stuff like the number of cores, hyperthreading, turbo and stuff. I'm not an expert about CPU by any stretch so I'm mostly comparing cost and the major features of the procs.
My brain can't wrap itself around how you'd upgrade CPU without shutting down VMs. I suppose it's because you shift all the VMs to another machine. Keeping in mind that I've never had vMotion ability with VMware because we just used Essentials. I've never even had shared storage so vMotion wouldn't have been very useful anyway since it would have required a massive data copy to another machine over 1GB ethernet first. I'm quite excited about the capabilities I'll gain going to XCP-NG.
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@CodeMercenary Yes, vMotion (Guest VM migration) and 10G ethernet are your friends... if you have enough spare resources and things are setup for migration.
With a pool you generally have shared VM storage on a NAS/SAN. That way when you migrate VMs from one host to another you are only moving the memory and the storage stays on the SAN. If you use local storage then the migration includes the storage and can take a long time if you have a large dataset. It does work but you need enough disk space on the other machine.
There are some shared host storage solutions, but not a point an click option at this time.
10G network cards and switches are very reasonably priced these days. I see the Dell R630/R730 10G X540 cards for $25USD.
For Intel Xeon E5 CPUs, the upgrade from v1->v2, and v3->v4, etc. is an incremental improvement and not a huge leap. Most of the Xeon systems support two generations of CPU. That's why you see the same server (by model) with different CPUs.
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Another option is to just manage several hosts but not have a pool, may not be ideal but just mentioning that it's entirely possible. It's the setup I use in my home lab actually, one XOCE managing 3 hosts of different CPU generations (all AMD but one is a 3970X and the others are 19XX series AMD units). It's all still managed pretty similarly to a pool and then you don't lose CPU features on any of the hosts.
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@CodeMercenary And you can still migrate VMs (and their storage) between hosts. Without shared storage a pool is not a lot of help. You still only need one XO setup and you can see everything there.
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Oh, that's great to know @planedrop and @Andrew. While live migration would be cool, I don't know when I'd be able to set up a SAN or have a NAS big enough, fast enough and with fast enough networking, to be able to keep my VMs on it. Knowing that I can just put them in different pools and I can still offline migrate them is cool.
Are there any downsides when it comes to backups if they are in different pools? I assume XO is fine with backing up VMs in one pool to a remote in another pool.
I'm planning to put 10GB ethernet in the R630 so the servers can all communicate fast. When it comes to the XCP restrictions about ethernet ports and such, that's only if they are in pools so using separate pools eliminates that problem too, right?
The R730XD arrived while I was typing this. It's gonna be a fun weekend. Already making plans to remove the current processor and get two better ones plus add more RAM (only has two 8GB sticks right now). Nice that processors that were $2500 when this server was built are now around $100.
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@Andrew said in Homogeneous pools, how similar do the CPUs need to be?:
@CodeMercenary ... The pool will use the features of the lowest CPU...
So this will make a pool of 5 machines with one old CPU use only the available features of the old CPU?
So if I need some newest cryptographic extensions for OpenVPN or something similar they will not be available on the whole pool if one server CPU does not support them?Is this to support migrations only? It would be better to just say "this guest from this host can not be migrated, it has to be shut down to move" or something similar.
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As soon you are in a pool, it's meant to live migrate VMs around. That's why all the CPU instructions will be limited to the lowest CPU.
If you don't want to do that, just don't pool your hosts together
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@CodeMercenary To answer your questions about backups, they should all be fine, the remote is attached to XO rather than the host itself so XO can backup any VM from any host it has access to, to any remote configured in XO.
