XenServer 8.0 - Major update due Q1 2019
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@olivierlambert How is this done?
I'm not talking about dynamic memory or Maximum vCPU when starting a virtual server.I'm talking about hotplug, add CPU / Memory even though the values are higher than configured in the VM. Hyper-V 2016 Generation 2 has already held this and VMWare a long time with Hotplug.
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How is this done? Just give a bigger vCPU max than current vCPU while the VM is off, same for static MAX for RAM. Xen and XenServer support this for a while and it works well. So I don't understand why you can't achieve it?
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@olivierlambert I think you missed the point that he wants the ability to do this while the VM is running
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And? Sure, you can do that, as long the VM is within the static min/max and under vCPU max settings. I'm using these features since I use Xen.
I'd really like to understand what's the limitation here. The only "recent" limit is the number of max vCPU can't be larger than total number of cores on the system, to avoid side channel attacks.
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Not using the latest XS/XCP-ng but at least until 7.1 LTSR it was impossible to change the values for a running VM (by GUI). They are disabled/greyed out.
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We had this feature exposed in Xen Orchestra since the start (or so). It's just that Citrix only added this in XenCenter recently. So it's more a client limitation done by Citrix than a real modification.
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Even with XOA, we have the same problem with XCenter. With vCPU the rule works because you set a usage limit and can increase to the maximum that the host supports.
But for memory, we have only the minimum and maximum and the dynamic memory feature, which allows only a better allocation of the entire host.
But imagine the situation where a customer hires an 8GB VM and then wants a feature upgrade, to 16GB, the increase can not be done "hot," with the server on, requiring a schedule to perform the upgrade.
In the case of VMWare, HOTPLUG is supported, that is, I can upgrade to 16GB without turning off the VM. I believe this is a limit on qemu, since all versions of Xen (Source) support hotplug for vCPU, RAM, Disk and Network,
In XOA:
VM_BAD_POWER_STATE(OpaqueRef:8727f5ec-37ad-4273-8130-a1c0df0ed96b, halted, running)
MEMORY_CONSTRAINT_VIOLATION(Memory limits must satisfy: static_min ≤ dynamic_min ≤ dynamic_max ≤ static_max) -
I don't see the problem: just extend the static memory to the max of the host capacity and with a dynamic max to the amount you need right now.
After a while, if you need more RAM, just raise dynamic max up to static max.
Am I missing something here?
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When I adjust the FIXED memory to 100GB, and the minimum dynamic to 40GB and maximum dynamic to 60GB.
But when I click Ok, the static memory gets the same value as the maximum dynamic.
At least in XenServer 7.1 CU2, the configuration you report does not work for me.
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Please try with Xen Orchestra. You should be able to have this setting done once for all when the VM is halted, and then enjoy to set within the whole dynamic setting while it's up.
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@olivierlambert said in XenServer 8.0 - Major update due Q1 2019:
Please try with Xen Orchestra. You should be able to have this setting done once for all when the VM is halted, and then enjoy to set within the whole dynamic setting while it's up.
I LOVE XOA! hehehehe
That'S exactly what I wanted.
Thanks so Much for the help and sorry for the persistence.
But See the problem, VM Guest recognizes total memory.
Is That a bug?
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I need to run some tests on XCP-ng, but IMHO you shouldn't be able to see the static max inside the VM. You should be able to see dynamic max.
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It's as expected in XCP-ng:
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I tested on other VMs and the memory displayed is always the maximum static.
Will a Bug on XS 7.1? -
Possible, dynamic memory management changed a lot since 7.1
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If I remember correctly what I read, I think Windows guests see all the memory (static max or dynamic max, I don't remember) but there's a special device that "eats" the memory that is not available to the VM, so that what's really available to it corresponds to the dynamic value (between dynamic min and dynamic max).
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It's dynamic max. But I'm pretty sure it was heavily changed in 7.2
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@stormi It has always been the way that the daemon of xentools bloated up, when you need to free up dynamic memory within the range. I just have 7.1 LTSR running, can't verify for any CR, right now.
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@olivierlambert I Did a test with the XS 7.6 and CentOS7 (HVM) and the memory calculation does not work correctly.
Sometimes it decreases the memory in the Guest VM, but never displays the values correctly. I am reinstalling the Host for XCP 7.6 and perform new tests. I'll open a new thread for that matter.
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Behavior should be the same in XS and XCP-ng 7.6
If you have lower than dyn max in your VM, it's due to pressure of other VMs on the host. Also during a live migration, Xen will "deflate" the VM to dynamic min to allow faster migration.
