How many domain controllers?

[joe90bass]

Please do not just demote the exchange box! you need to find out the correct order to do it in as it looks like it's different for exchange.

Agreed, DON'T DO IT!! See here
I'm sure it is possible if you read up and test beforehand, personally I'd leave it alone though!

[stephen_o]

You should really have at least 2 domain controllers for each site. I would suggest doubling up on DNS and DHCP too. You should also be aware that if your Global Catalogue server goes down, Exchange will go down too so making both DC`s global catalogues is also a plan. on a network of this size, the replication traffic would be minimal so it wouldn`t hurt.

[torledo]

Can you real-time mirror a running Windows virtual server's disks to a second physical server without needing a second license? You'll need the license for the one virtual Windows server, obviously, but surely the mirror is simply a backup until the first physical server conks out and the second physical server starts actually running the virtual server image?

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David Hicks

It's really beyond me why anyone would want to use virtual server for any production environment....even hyper-v, which is microsofts real stab at quasi-enterprise virtualization is not all that impressive.

hyper-v does do high availability in the Active/Standy (A/S) sense using shared SAN storage, but that's really based on the new and improved cluster services engine in w2k8 and it's built-in fault tolerance capability rather than a specific vm HA product like Vmwares HA...hyper-v doesn't have live, uninterrupted VM mobility such as a vmotion-type implementation....but the mobility solution it does have should allow customers to migrate VM's to new hardware with a downtime of around 15 seconds before everything is back to an online state (the delay means it's 'quick migration' rather than 'live migration'). In some cases that's not acceptable, but many companies who'd like the cheapness of an out-of-the-box virtualization solution it's not a dealbreaker.

Leave virtual server for the training lab is my advice, and it doesn't sound unreasonable to me that a standy in any A/S clustering or HA solution should need to be licensed. It's common in certain parts of the commercial unix world (where you pay through the nose for such solutions for both clustering engine, application-specific extensions AND multipathing software) - why should MS be any different, they're already giving a ton of stuff away virtually for next-to-nothing depending on the type of agreement you utilise for purchase.

[SteveMC]

Agreed, DON'T DO IT!! See here
I'm sure it is possible if you read up and test beforehand, personally I'd leave it alone though!

We've just cleaned up a similar situation (Exchange running on a DC) - the simplest way is to install a temporary server with Exchange, migrate the mailboxes and public folders (including the system folders) over, then demote the original server, reinstall it with Exchange and migrate back again.

It does take a while to do though, and you need to be sure that replication works between the two Exchange servers (don't use smarthosts in the config, you have to use SMTP connectors).

[torledo]

Right, checked again, and he went back and asked Microsoft. It seems we simply have to license each physical machine for as many copies of Windows Server 2008 Standard that each physical machine has on it, even if those copies aren't actually running. So if we have one machine running Windows Server, with live mirroring to another physically separate server, we have to get two Windows Server licenses. I rather get the feeling that the licensing simply hasn't been thought through all that clearly as it seems a bit much to have to pay for two whole server instances when we'll only ever be running one, but said licenses are still only £100 each so we can't grumble too much.

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David Hicks

i think you mean live mobility, 'mirroring' is really a traditional clustered or HA solution where OS instances are installed on the machines in the cluster but one or more machines remain idle as in clustered Active-Standy....i agree that the live mobility should not be tied to physical machines but should be implemented based on unlimited virtualization rights as dmccoy described with datacenter edition.

[dhicks]

it doesn't sound unreasonable to me that a standy in any A/S clustering or HA solution should need to be licensed.

Oh, indeed, but not at 100% of the cost of the live server - maybe 20%? As it happens, for our situation - point-to-point replication of disk images - it's not so bad, but you can see costs getting out of control (exponentially, literally) if you have the whole SAN-and-multiple-processing-machines setup.

'mirroring' is really a traditional clustered or HA solution where OS instances are installed on the machines in the cluster but one or more machines remain idle as in clustered Active-Standy

Yep, that's what we have - disk images are mirrored in real time, but not actual VM state. If a physical server went down we would have to boot up copies of the VMs on the backup server, so we don't have instant failover, it'd take us a few minutes to get back up. It's maybe something I'll look at in my Copious Free Time over the summer :-)

i agree that the live mobility should not be tied to physical machines but should be implemented based on unlimited virtualization rights as dmccoy described with datacenter edition.

I don't think that would help us - we're not running VMs on top of Windows, we're running VMs on top of CentOS + Xen. I'd like to be able to simply pay for a copy of Windows Server 2008 that I can run in a virtual machine and move around as needed between physical machines. Fine if we need to pay a bit more than just for standard edition (maybe £150 for "VM Edition"?), but the current situation seems as though if you want any sort of live failover facility based entirely on Windows Server you have to buy datacentre edition for each processing machine, plus pay for whatever third-party stuff you need to get Windows to be able to mirror disk volumes accross a network or act as an iSCISI server if you're using a SAN. Microsoft are looking a bit behind the times here - also, how do you handle licensing pre-built VM images based on Windows?

Sorry, we're wandering off topic here - we'd better nip over to the virtual machines forum if we want to winge any more about Microsoft's overly-complex licensing issues!

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David Hicks

[torledo]

Oh, indeed, but not at 100% of the cost of the live server - maybe 20%? As it happens, for our situation - point-to-point replication of disk images - it's not so bad, but you can see costs getting out of control (exponentially, literally) if you have the whole SAN-and-multiple-processing-machines setup.



Yep, that's what we have - disk images are mirrored in real time, but not actual VM state. If a physical server went down we would have to boot up copies of the VMs on the backup server, so we don't have instant failover, it'd take us a few minutes to get back up. It's maybe something I'll look at in my Copious Free Time over the summer :-)


I don't think that would help us - we're not running VMs on top of Windows, we're running VMs on top of CentOS + Xen. I'd like to be able to simply pay for a copy of Windows Server 2008 that I can run in a virtual machine and move around as needed between physical machines. Fine if we need to pay a bit more than just for standard edition (maybe £150 for "VM Edition"?), but the current situation seems as though if you want any sort of live failover facility based entirely on Windows Server you have to buy datacentre edition for each processing machine, plus pay for whatever third-party stuff you need to get Windows to be able to mirror disk volumes accross a network or act as an iSCISI server if you're using a SAN. Microsoft are looking a bit behind the times here - also, how do you handle licensing pre-built VM images based on Windows?

Sorry, we're wandering off topic here - we'd better nip over to the virtual machines forum if we want to winge any more about Microsoft's overly-complex licensing issues!

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David Hicks

right, i'm a bit confused, my understanding was that a single windows server enterprise 2003/2008 license would allow you to install it up to four times on a machine (irrespective of number of processors) without paying for licensing of each additional instance - so you buy windows server 2008 and can install it four times....if that's the case do you need to request a VLK for each instance of the OS you plan to install for VM usage, even though you've not purchased those additional licenses ?

if you require more than four instances do you then have to pay to license each additional instance of windows server 2008 running in a VM ?

Moving on to windows datacenter edition....windows datacenter is licensed per socket and allows you to install unlimited number of VM's that the machine can handle at no additional cost. Because it's licensed per socket, setting up a hypervisor on a four socket box has a high upfront cost because of the relatively high per processor price, but the value is in that you can install 5, 10, 15 whatever is technially feasible without paying any additional licensing cost beyond that initial single datacenter license purchase.

IF that's the case, datacenter is great value, and enterprise isn't a bad deal.

Even a HA solution, even though it means you're paying twice for the privildge of runing idle machine(s), it's still decent value i think.

However if you have to pay for each windows VM instance, then obviously it's not good value.

[dhicks]

my understanding was that a single windows server enterprise 2003/2008 license would allow you to install it up to four times on a machine

On a physical machine running Windows and Hyper-V, quite possibly. However, we're running a bunch of CentOS + Xen machines. This is the problem - everyone I speak to assumes we want to run Windows VMs under Windows. We don't want to do that as it costs lots of money to do properly - £300-odd per machine for Windows Server 2008 Datacentre Edition, then you've got to pay on top of that for a third-party solution of some kind to replicate disks between physical machines or pay for a SAN with an iSCISI target. We just want to run one copy of Windows Server as a domain controller, which we want to mirror to a separate physical server in case of server failure.

There is one solution - run Windows Datacentre on top of Xen, then run Windows VMs on top of Windows Datacentre. But that would just be silly...

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David Hicks

[DMcCoy]

right, i'm a bit confused, my understanding was that a single windows server enterprise 2003/2008 license would allow you to install it up to four times on a machine (irrespective of number of processors) without paying for licensing of each additional instance - so you buy windows server 2008 and can install it four times....if that's the case do you need to request a VLK for each instance of the OS you plan to install for VM usage, even though you've not purchased those additional licenses ?

if you require more than four instances do you then have to pay to license each additional instance of windows server 2008 running in a VM ?

Moving on to windows datacenter edition....windows datacenter is licensed per socket and allows you to install unlimited number of VM's that the machine can handle at no additional cost. Because it's licensed per socket, setting up a hypervisor on a four socket box has a high upfront cost because of the relatively high per processor price, but the value is in that you can install 5, 10, 15 whatever is technially feasible without paying any additional licensing cost beyond that initial single datacenter license purchase.

IF that's the case, datacenter is great value, and enterprise isn't a bad deal.

Even a HA solution, even though it means you're paying twice for the privildge of runing idle machine(s), it's still decent value i think.

However if you have to pay for each windows VM instance, then obviously it's not good value.

I assume it would work like standard in that you have to license the machine multiple times for each of the potential windows server licenses it holds. It get really complicated with enterprise really, as each of the additional instances belongs to the base license, so if it's not really got to any further than standard!

So I have 2 big servers, 8 VMs on one. I have 2 enterprise licenses for it. Now, I can buy just one license for the second server, and I can migrate 4 VMs, but only those from *one* base license! Complicated isn't it! Tracking to stay *technically* within the exact license terms is nearly impossible.

Datacenter (academic) is much better value than it was, considering you could be licensing 2 sockets and have 8 cores! Mine are still dual socket, single cores

It also applies to things like Exchange, and other MS server products. This can vary though. I simply don't move my exchange box around much.

Virtualisation isn't a method of saving money as you know, but this is often forgotten after just looking at the savings on the number of physical boxes. It's just for consolidation and dynamic provisioning really, with some extra things thrown in.

[DMcCoy]

On a physical machine running Windows and Hyper-V, quite possibly. However, we're running a bunch of CentOS + Xen machines. This is the problem - everyone I speak to assumes we want to run Windows VMs under Windows. We don't want to do that as it costs lots of money to do properly - £300-odd per machine for Windows Server 2008 Datacentre Edition, then you've got to pay on top of that for a third-party solution of some kind to replicate disks between physical machines or pay for a SAN with an iSCISI target. We just want to run one copy of Windows Server as a domain controller, which we want to mirror to a separate physical server in case of server failure.

There is one solution - run Windows Datacentre on top of Xen, then run Windows VMs on top of Windows Datacentre. But that would just be silly...

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David Hicks

I wouldn't complain too much about £300 for datacenter, have you seen what everyone else has to pay for it?

[OverWorked]

For MS Server licensing see this MS blog post.

Believe it or not, somewhere there's a video of a father explaining MS Server licensing to his 6 year old daughter with sweets. Can't find it now - I'll see if I can dig it out.

To get back to the original question: You should have no less than 2 DC's. The work involved in restoring AD when your one and only DC has a catastrophic failure doesn't bear thinking about. I know - I was in that position once. Since then I've always had 2 DCs.

Make both of them global catalogue servers. If the PDC emulator goes down, it's easy enough to make the other one seize roles, while you quickly build another server and make that another DC, bringing your total back to 2.

I think 2 would be enough for a school.

[DMcCoy]

This has the answers to most things, and is a clarification of previous license terms etc.

http://download.microsoft.com/downlo...tion_brief.doc

[dhicks]

my understanding was that a single windows server enterprise 2003/2008 license would allow you to install it up to four times on a machine (irrespective of number of processors) without paying for licensing of each additional instance - so you buy windows server 2008 and can install it four times....

Just read through the .doc file and the blog post above. Yes, that seems to be about right...

[if that's the case do you need to request a VLK for each instance of the OS you plan to install for VM usage, even though you've not purchased those additional licenses?

...except that the blog post doesn't get around to answering that question. Hmm. Good point...

Even a HA solution, even though it means you're paying twice for the privildge of runing idle machine(s), it's still decent value i think.

Yes, pretty decent (especially at the academic pricing we get :-)). Really, we might as well get Enterprise or Datacenter, as it's kind of a buy-three-get-one-free deal by then.

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David Hicks

[OverWorked]

For MS Server licensing see this MS blog post.

Believe it or not, somewhere there's a video of a father explaining MS Server licensing to his 6 year old daughter with sweets. Can't find it now - I'll see if I can dig it out.

Duhh... The video I was looking for is on the same blog posting. It's worth watching, though.