Trying out Xen
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I never though of using Ubuntu as Dom0 all of the documentation I read when getting everything setup recommended letting the installer create Dom0 for you.
Isn't that best practice, rather than installing your own Dom0?
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@scottalanmiller said:
No, that's not a good description. It converts the running Ubuntu instance into the Dom0. Exactly how HyperV works as well.
I thought the standalone HyperV didn't have a Dom0 OS - that it was exactly like ESXi, just a smallish Baremetal install.
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@Dashrender said:
I thought the standalone HyperV didn't have a Dom0 OS - that it was exactly like ESXi, just a smallish Baremetal install.
Nope, nothing would work that way for two reasons:
- You would never offer the penalty of a Dom0 if you didn't need it. That would be crazy. Getting to VMware's approach is the holy grail of hypervisor design.
- You would never engineer a product in two ways like that, it would cost a fortune.
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This is the patching scripts we use in our Environment (work and personal) https://github.com/dalgibbard/citrix_xenserver_patcher
Love this platform, just so many amazing items.
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@scottalanmiller said:
@Dashrender said:
I thought the standalone HyperV didn't have a Dom0 OS - that it was exactly like ESXi, just a smallish Baremetal install.
Nope, nothing would work that way for two reasons:
- You would never offer the penalty of a Dom0 if you didn't need it. That would be crazy. Getting to VMware's approach is the holy grail of hypervisor design.
- You would never engineer a product in two ways like that, it would cost a fortune.
Wow - not that I don't believe you, but well - I guess I don't. I'll have to try this for myself.
The reason I say this is because you can install HyperV without a Windows Server license, but I don't think you can install HyperV 'as a service' in a pre existing Windows Server install without one.
If you are forced to get a Dom0 Windows VM with HyperV, then how can you avoid the license requirement?
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@DustinB3403 said:
I never though of using Ubuntu as Dom0 all of the documentation I read when getting everything setup recommended letting the installer create Dom0 for you.
Isn't that best practice, rather than installing your own Dom0?
This is all misunderstanding of how Xen works. There is one and only one way to install Xen. A Linux (or NetBSD) OS is installed. Xen installation takes that existing OS and assigns it as Dom0. Xen is installed and set to boot. System reboots to Xen with the former OS as the Dom0.
Ubuntu, OpenSuse, roll your own, XenServer... they all do this identically.
HyperV is the same. No matter what version you choose or how it appears you are installing, the exact same process happens.
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@DustinB3403 said:
Isn't that best practice, rather than installing your own Dom0?
You can't install your own Dom0 in the way that you are thinking. The original OS is always the Dom0. Has to be because that is where the drivers and such are.
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@scottalanmiller said:
@DustinB3403 said:
Isn't that best practice, rather than installing your own Dom0?
You can't install your own Dom0 in the way that you are thinking. The original OS is always the Dom0. Has to be because that is where the drivers and such are.
Holy cow - that statement has answered a question I've had forever regarding how drivers are handled in HyperV vs ESXi... thanks for that!
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@scottalanmiller said:
@DustinB3403 said:
oh and Scott at my home lab I setup Xen to a 16GB flash without any issues at all, it was very, very easy to do.
I know that @Mike-Ralston was working on that a bit and was having issues with the install. Maybe he didn't try between 6.2 and 6.5.
Would it be just as advantageous to use a small ssd? Like a 24 gig mSATA or something?
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@johnhooks said:
Would it be just as advantageous to use a small ssd? Like a 24 gig mSATA or something?
Not from a technology standpoint. Only if you owned it already and it was useless and just laying around.
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@johnhooks said:
@scottalanmiller said:
@DustinB3403 said:
oh and Scott at my home lab I setup Xen to a 16GB flash without any issues at all, it was very, very easy to do.
I know that @Mike-Ralston was working on that a bit and was having issues with the install. Maybe he didn't try between 6.2 and 6.5.
Would it be just as advantageous to use a small ssd? Like a 24 gig mSATA or something?
That would require an mSATA port in the server and cost more than a SD card or USB stick - so why bother with the expense?
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@Dashrender said:
The reason I say this is because you can install HyperV without a Windows Server license, but I don't think you can install HyperV 'as a service' in a pre existing Windows Server install without one.
What does the license have to do with the technology?
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@Dashrender said:
@johnhooks said:
@scottalanmiller said:
@DustinB3403 said:
oh and Scott at my home lab I setup Xen to a 16GB flash without any issues at all, it was very, very easy to do.
I know that @Mike-Ralston was working on that a bit and was having issues with the install. Maybe he didn't try between 6.2 and 6.5.
Would it be just as advantageous to use a small ssd? Like a 24 gig mSATA or something?
That would require an mSATA port in the server and cost more than a SD card or USB stick - so why bother with the expense?
The drives are only around ~$20-$30. Same for the enclosure. I just figured you'd gain some performance from it.
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@scottalanmiller said:
@Dashrender said:
The reason I say this is because you can install HyperV without a Windows Server license, but I don't think you can install HyperV 'as a service' in a pre existing Windows Server install without one.
What does the license have to do with the technology?
Nothing of course - but legally you can deploy HyperV without owning a single Windows Server license. If what you're saying about Dom0 is true though - wouldn't that be a Windows install, and therefore require a server license?
Now perhaps it's not a full windows install, instead it's a core install, but not core, some super stripped down core install that can't be made to do anything else, and therefore bypassing the licensing issue.
And I'll fully admit that's completely plausible.
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@Dashrender said:
If you are forced to get a Dom0 Windows VM with HyperV, then how can you avoid the license requirement?
Because you don't "get" a Dom0. The HyperV installer obviously creates it as part of the process or would not work, just like ESXi did before ESXi 5 when they would create a Dom0 and put RHEL 2.1 into it. It was part of the package.
HyperV's included Dom0 is not Windows Server or Windows Desktop, it is an incredibly stripped Windows OS that is not available on its own in any way. It exists only with HyperV and there is no Microsoft licensing associated with it. You can't do anything with it except for manage HyperV, which if you look at MS licensing is always free, no matter how you acquire the Windows instance that you are using as the Dom0 it always ends up free. This is why. The licensing is consistent and incredibly straightforward, as long as you understand what is going on. If you fight the "Dom0" idea, all MS licensing becomes insane and makes no sense and there is no way to predict it.
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@johnhooks said:
@Dashrender said:
@johnhooks said:
@scottalanmiller said:
@DustinB3403 said:
oh and Scott at my home lab I setup Xen to a 16GB flash without any issues at all, it was very, very easy to do.
I know that @Mike-Ralston was working on that a bit and was having issues with the install. Maybe he didn't try between 6.2 and 6.5.
Would it be just as advantageous to use a small ssd? Like a 24 gig mSATA or something?
That would require an mSATA port in the server and cost more than a SD card or USB stick - so why bother with the expense?
The drives are only around ~$20-$30. Same for the enclosure. I just figured you'd gain some performance from it.
Once the hypervisor loads it rarely goes back to disk - it runs from RAM.
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@Dashrender said:
@johnhooks said:
@Dashrender said:
@johnhooks said:
@scottalanmiller said:
@DustinB3403 said:
oh and Scott at my home lab I setup Xen to a 16GB flash without any issues at all, it was very, very easy to do.
I know that @Mike-Ralston was working on that a bit and was having issues with the install. Maybe he didn't try between 6.2 and 6.5.
Would it be just as advantageous to use a small ssd? Like a 24 gig mSATA or something?
That would require an mSATA port in the server and cost more than a SD card or USB stick - so why bother with the expense?
The drives are only around ~$20-$30. Same for the enclosure. I just figured you'd gain some performance from it.
Once the hypervisor loads it rarely goes back to disk - it runs from RAM.
Oh, I misunderstood. Ok, makes more sense.
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@johnhooks said:
The drives are only around ~$20-$30. Same for the enclosure. I just figured you'd gain some performance from it.
Nope, less than one second, on system boot only, is the best case advantage and likely not even that.
Based on VMware ESXi but the logic still applies:
http://mangolassi.it/topic/5392/why-we-run-vmware-esxi-from-sd-or-usb
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@Dashrender said:
Now perhaps it's not a full windows install, instead it's a core install, but not core, some super stripped down core install that can't be made to do anything else, and therefore bypassing the licensing issue.
Exactly. Microsoft has the included stripped option for "pure" HyperV installs. They have a desktop option for controlling with Windows 8 or higher. And they have a server option for controlling with Windows Server. All of which are free!!
Obviously the included one with HyperV is the best as it is the lightest and most stable/secure and requires the fewest patches. Hence why installing the "free" HyperV has always been recommend even when you own Windows Server licenses.
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@scottalanmiller said:
@Dashrender said:
Now perhaps it's not a full windows install, instead it's a core install, but not core, some super stripped down core install that can't be made to do anything else, and therefore bypassing the licensing issue.
Exactly. Microsoft has the included stripped option for "pure" HyperV installs. They have a desktop option for controlling with Windows 8 or higher. And they have a server option for controlling with Windows Server. All of which are free!!
Obviously the included one with HyperV is the best as it is the lightest and most stable/secure and requires the fewest patches. Hence why installing the "free" HyperV has always been recommend even when you own Windows Server licenses.
OK great, thanks for the explanation - and I now know how the driver thing is handled in HyperV for the hardware.... damn that one's haunted me for several years.
