Where to start creating a virtual server setup? RM CC4 to Vanilla

[tj2419]

Hi

 

I am starting to do research into migrating our CC4 network to a windows vanilla network. We are also thinking of moving to a virtual server setup. Been playing around with XenServer recently and love it.

 

CURRENT SETUP

 

2 Domains - Admin & Curriculum (The way its been set up by the LEA)

 

ADMIN DOMAIN

Admin SVR1 - DHCP, DNS, SIMS Server, FMS, User workareas and shared drives stored locally. about 25 admin/office staff

 

CURRICULUM DOMAIN

Curriculum SVR 1 - DHCP, DNS, All Staff accounts work areas, two shared drives, Software running off a RMPublic drive.

Curriculum SVR 2 - DNS, Half of the student accounts

Curriculum SVR 3 - DNS, Half of the student accounts

NAS BOX 1 - Two file shares for staff and students.

 

Questions

1. How would you set it up if you were virtualising? How many hosts? SAN? Switch links to SAN? DC's?
   
2. How do you decide which services to split across the servers?
   
3. Where do you keep your user directories? SAN or DC?
   

 

SUGGESTION

One suggestion is to leave the admin network as it is as we currently only really want to mess with one network at a time. Get it fully working and then merge the two networks. (Current admin network is vanilla but set up by LEA)

 

- Two Hosts running VM ware 5 both having a DC on there.

- Have one host mirrored to the other for HA.

- SAN storing all the shared areas and user areas.

 

or

- Three hosts running VM ware 5 to offer more resilience.

- SAN storing all the shared areas and user areas.

 

As you can probably see its a very new area for me. Quite happy managing networks but setting up from scratch especially on a virtual setup is a new one

 

Any advice would be great thanks.

[mrbios]

You need to go back a few steps and really design your network before you jump in to planning virtualisation from the point you're at to be honest. ......of course you could just buy some hosts, virtualise what you have with P2V and setup some SAN storage but lets be honest, from the point your network is at i think it needs redesigning to bring it in to 2013...at the moment you're more Y2K, but that's the LEAs fault.

 

Are all your switches managed and vlan capable?

How many PCs, printers etc does your network have?

How many users?

What's your wireless like? Are you going to want a managed wireless setup in the future?

Moving to virtualisation most likely means a new backup and recovery strategy

Have you explored the potential of Hyper-V, Xen and VMware to conclude as to which is the best product for your uses? (Honestly these days if your licensing works out effective then Hyper-V is a fantastic competitor and big money saver compared to VMware now, and i say that as someone who has praised VMware since the day i started using it)

What sort of licensing structure are you under? (volume licensing, OVS, EES etc?)

 

there's probably more but that's all i can think of off the top of my head, also have you been given an increased budget to deal with this change or is it just something you've decided to do?

 

I'd highly recommend bringing a consultant in to help you if you haven't had to do this before (which can sometimes mean a swallowing of pride, depends on the type of person you are and how confident you feel to do the work though) a good one will teach you what they're doing and why as they go through things with you too and often advise you of changes and let you do them yourself rather than simply doing them (Which also works out cheaper for you seeing as these people work on hourly rates)

 

FYI i started with almost the exact same type of network 7 years ago, went through the same scenario, had a consultant help....and while i may not know exactly "how" to design a network in a major change such as this, i certainly feel confident in saying i know how NOT to do it

 

ALTERNATIVELY

You go with one of your suggestions, which aren't bad ideas by any means. How you choose to store both user data and virtual machine data depends on the setup you go for though. For example if you want to be able to do live migrations of virtual machines between hosts then those hosts need to be able to see a shared storage point, be that FC or iSCSI etc. (Personal view..iSCSI is a lot more flexible and generally cheaper). Say in the scenario where you have two hosts in a HA cluster, both sharing the same VM store, if one host dies the vms from the dead host will instantly be switched over to the working server and powered back up by the cluster manager (or vCenter in vmwares case) also if you're virtualising your file server you need to choose what device your file storage is goign to be on (don't store it in the virtual machine!!) and how your'e going to present it to the VM, which again depends on a few factors.

 

EDIT: hopefully my comments are useful and correct, hopefully other geeks will add or adjust (maybe even correct in places) what i've said though, my brains frazzled today.

Edited November 12, 2013 by mrbios

[tj2419]

Hi MrBios thanks for the detailed response.

 

As you can tell this would be my first time designing / creating a network. Managed a few but never created. I don't really like having the split domain but like i said i really want to leave the admin network till i have a stable vanilla network of my own and then merge them.

 

In answer to the questions

 

Are all your switches managed and vlan capable?

We had New HP 1910v switches fitted a year ago. Fibre backbone

 

How many PCs, printers etc does your network have?

400 desktops, 80 laptops, 80 ipads on curriculum and 25 desktops on admin.

 

How many users?

1300 users in total

 

What's your wireless like? Are you going to want a managed wireless setup in the future?

New Ruckus wireless installed summer 2013

 

Moving to virtualisation most likely means a new backup and recovery strategy

Currently have backup exec but have been looking at buying into veeam as a backup solution. We have disk to disk to tape autoloader currently.

 

Have you explored the potential of Hyper-V, Xen and VMware to conclude as to which is the best product for your uses? (Honestly these days if your licensing works out effective then Hyper-V is a fantastic competitor and big money saver compared to VMware now, and i say that as someone who has praised VMware since the day i started using it)

We are playing around with xenserver the open source one but i just worry about building a whole network on an open source solution. Would look at hyper-v again as i was looking for vmware after discussions with suppliers and local schools but need to sit down and compare them properly.

 

What sort of licensing structure are you under? (volume licensing, OVS, EES etc?)

Microsoft EES agreement for Desktop OS, Office.

 

Thanks

[kevin_lane]

Yea I a agree with mrbios creating a virtual environment with fail over hosts with HA and a csv or cvs can never remember and also knowing what qourm you want is going to be difficult

 

I didn't get a consultation however I did speam to people but majority o spent was going through visio and Microsoft training book it

 

And also if you are having multiple host you also need to think of the bigger picture too such as power failure and redundancy its not easy also you need to think about ur switch gear do you want all going through your main switch or are you going to have separate switches

 

Are you going with a 2008r2 cluster or are you going with 2012

 

Hope I haven't scared you but you have to plan every stage but ita definitely fun even though sometimes I was wondering are the hosts ok have a put in enough resources or should I brought that extra 10gig of ram lol

[mrbios]

In answer to the questions

 

Ah a lot of good stuff there then, you're more up together than i thought really. (I read admin + curric networks, and instantly expect something from the ark ) Very similar in size to myself then so i have some idea of what you're dealing with, same amount of users, laptops and ipads and only 200-300 PCs less.

 

Personally i think in your position I think i'd feel both Hyper-V and VMware are the right choice, so you can't really go wrong, both are competing well on features in their latest versions, both have a good history for stability. Performance while in favor of vmware isn't far off on Hyper-V either but it's negligible on the scale we're using it at. Worth trialing both and seeing what you find easier to work with.

 

Have you made much use of vlans yet?

 

What make/model is your current NAS box and what's it running in terms of array and disks?

 

Which version of backup exec are you on?

[twin--turbo]

Although I hate to say it, with XenServer Now having all it's features in the free licence it's a reasonable choice for small scale deployments where you want HA.

 

I do much prefere vSphere though.

 

Rob

[tj2419]

Haha yer not too too bad. Been doing a lot of updating recently. Tried proposing a switch from two domains a while back but LEA scared the school leaders into thinking its a bad idea. So the plan is to create a quick, robust and reliable network and then propose the merging again.

 

Having a play around with VLANS at the moment. Setting up BYOD on a ruckus wireless with a smoothwall (opensource) box. Proving interesting but my first go at vlanning.

 

NAS is about 6 years old RM NAS ONE i think the model. 1TB storage set up in RAID 0.

 

Backup exec we are on 2010. I've seen the newer versions seem to handle vm backups but it just seems overly bulky for what we need.

 

What i cannot get my head around is how you make the decision over number of hosts? Number of DC's and the best strategy for storing the user directories. (On the DC's or SAN?)

 

Cheers

[kevin_lane]

Well that's depending on how you want your new structure to be personally I don't put dcs on our hosts because I don't like the idea but I know people have

[tj2419]

Well that's depending on how you want your new structure to be personally I don't put dcs on our hosts because I don't like the idea but I know people have

 

How do you have yours set up?

 

Thanks

[Jamo]

Haha yer not too too bad. Been doing a lot of updating recently. Tried proposing a switch from two domains a while back but LEA scared the school leaders into thinking its a bad idea. So the plan is to create a quick, robust and reliable network and then propose the merging again.

 

Having a play around with VLANS at the moment. Setting up BYOD on a ruckus wireless with a smoothwall (opensource) box. Proving interesting but my first go at vlanning.

 

NAS is about 6 years old RM NAS ONE i think the model. 1TB storage set up in RAID 0.

 

Backup exec we are on 2010. I've seen the newer versions seem to handle vm backups but it just seems overly bulky for what we need.

 

What i cannot get my head around is how you make the decision over number of hosts? Number of DC's and the best strategy for storing the user directories. (On the DC's or SAN?)

 

Cheers

 

 

Can I just say:

 

It may be time to look at getting that 1TB NAS retired!!!!! 6 years old and RAID 0??!?!??!?!?!?!?!?!

 

Thing to look at is your overall needs. How many user accounts, how many concurrent log ons. What is the state of the surrounding network infrastructure.

 

I used to work at a school, 3 ESXi hosts, 2 for main production and one which sat as a DR site across the road in the 6th form. ~70GB ram per host, roughly 30 servers in total between the boxes. I would say max contention (and this is max you would really want to go) is 20 - 30 VMs per host, any more and you start to run out of horsepower, however this rewally depends on your usage patterns.

 

In terms of storage always go SAN with virtual hosts, unless you are SERIOUSLY stuck with budget. SAN gives you much more freedom in terms of host migration between the hosts, plus better resiliency. I have seen the Dell's Equallogic series, (we use PS6100 atm at my current work, not a school though) and performance is really good.

 

For backup, take a look at Veeam for VM's, I think by far the easiest and performance is really really good.

 

User directories, depends on what you want to acheive, with VM's you aren't limited to one box many functions, if you want to split up servers for specific tasks then its really easy to do so. These days I don't see any reason not to put DC's in a virtual environment, for backup/restore and just general ease of maintenance it would be crazy not to!

[mrbios]

What i cannot get my head around is how you make the decision over number of hosts? Number of DC's and the best strategy for storing the user directories. (On the DC's or SAN?)

 

How many VMs do you expect to be running? and what heavy duty VMs will you be running (SQL for sims, fms etc for one) what about exchange, SCCM etc? How many hosts you have depends on the amount of things you need to run on them really.

 

I can just about fit my entire network on to two hosts, so i've gone for 4 hosts total. Mainly to spread the load but secondly so that it gives me significant headroom in the event of a hardware failure. This also enables me to move all my VMs around live, in order to free up a host for an update or restart.

 

As for how many DCs....everyone seems to do it differently, i'll leave that for someone else to answer because I'm not entirely sure. I've got a DC per client based subnet here, which totals 9 (two infrastructure ones - pdc and bdc, 1 wireless) our site is spread over 6 different buildings though so it made sense pre-virtualisation, not sure if it still does mind.

 

As for storage strategy's, that's a complex one, as there's a lot of variables at play and lots of different right ways of doing it. I can only speak from experience, and my experience has been of a scenario that works very very well....iSCSI SAN, 4 connections setup in two trunks, each trunk is it's own iSCSI vlan. I've got iSCSI Vlan 1 and iSCSI Vlan 2, then i've got two switches dedicated to iSCSI connections (V1910s infact!) for their specific vlans which the hosts are then connected to along with a trunk to the core. Every host sees both iSCSI vlans and every host see's the exact same storage configuration. Additionally every hosts network connections are identical (this is a requrement for vMotion and Storage vMotion to work).

 

Then on top of that I use another 16 bay iSCSI unit with 14 disks in a RAID10 + 2 hot spares. Two partitions one for user directories and one for the rest of the shares we have on the network. That iSCSI unit can either be connected in the same way as the VM storage as an RDM to vmware, or in my case i've got it setup with the windows iSCSI initiator to my VM.

 

...... Easiest way i could think of to explain it is to explain my setup seeing as i know it like the back of my hand. That's just one way of doing this though, you can do the same thing with a fibre channel storage unit, albeit i think you sacrifice some flexibility in favor of performance. You'd need to evaluate what sort of IOPS you require out of your storage to know what you need to be buying too.

 

Lastly tiered storage! For the file storage, SAS disks are good, but for VMs don't bother with them, cheap SATA disk sfor the low IOP stuff, consumer SSDs for the high IOP stuff (in raid 6 for resilience).

 

EDIT: Jamo makes a VERY good point there, RAID0!? Talk about living on the edge!

 

Another thing @Jamo just reminded me of... talking of DCs + backups + virtualisation, as someone just stepping in to virtualisation for the first time, this is a handy read to make sure you never do this wrong: http://social.technet.microsoft.com/Forums/windowsserver/en-US/a6ed40b2-1aa3-4431-8717-91b5d07065af/snapshots-and-domain-controllers-are-they-always-bad?forum=winserverhyperv

Edited November 12, 2013 by mrbios

[Jamo]

How many VMs do you expect to be running? and what heavy duty VMs will you be running (SQL for sims, fms etc for one) what about exchange, SCCM etc? How many hosts you have depends on the amount of things you need to run on them really.

 

I can just about fit my entire network on to two hosts, so i've gone for 4 hosts total. Mainly to spread the load but secondly so that it gives me significant headroom in the event of a hardware failure. This also enables me to move all my VMs around live, in order to free up a host for an update or restart.

 

As for how many DCs....everyone seems to do it differently, i'll leave that for someone else to answer because I'm not entirely sure. I've got a DC per client based subnet here, which totals 9 (two infrastructure ones - pdc and bdc, 1 wireless) our site is spread over 6 different buildings though so it made sense pre-virtualisation, not sure if it still does mind.

 

As for storage strategy's, that's a complex one, as there's a lot of variables at play and lots of different right ways of doing it. I can only speak from experience, and my experience has been of a scenario that works very very well....iSCSI SAN, 4 connections setup in two trunks, each trunk is it's own iSCSI vlan. I've got iSCSI Vlan 1 and iSCSI Vlan 2, then i've got two switches dedicated to iSCSI connections (V1910s infact!) for their specific vlans which the hosts are then connected to along with a trunk to the core. Every host sees both iSCSI vlans and every host see's the exact same storage configuration. Additionally every hosts network connections are identical (this is a requrement for vMotion and Storage vMotion to work).

 

Then on top of that I use another 16 bay iSCSI unit with 14 disks in a RAID10 + 2 hot spares. Two partitions one for user directories and one for the rest of the shares we have on the network. That iSCSI unit can either be connected in the same way as the VM storage as an RDM to vmware, or in my case i've got it setup with the windows iSCSI initiator to my VM.

 

...... Easiest way i could think of to explain it is to explain my setup seeing as i know it like the back of my hand. That's just one way of doing this though, you can do the same thing with a fibre channel storage unit, albeit i think you sacrifice some flexibility in favor of performance. You'd need to evaluate what sort of IOPS you require out of your storage to know what you need to be buying too.

 

Lastly tiered storage! For the file storage, SAS disks are good, but for VMs don't bother with them, cheap SATA disk sfor the low IOP stuff, consumer SSDs for the high IOP stuff (in raid 6 for resilience).

 

EDIT: Jamo makes a VERY good point there, RAID0!? Talk about living on the edge!

 

 

I would say 9 DC's is quite a lot! 2 or 3 is ideal for a school I would have thought. Mainly for resiliency. Unless you have a multi site (ie across WAN connections) having DC's in different buildings/subnets isn't a requirement. On the other hand it won't hurt, just not sure it would provide any benefit.

 

I do also have to mention the golden rule of DCs on a VM platform...

 

Never snapshot and restore a domain controller. Else you will experience the most weird behaviour...

 

 

Edit: lol just noticed that was in the article above!!

 

Do note though that Veeam support restoring Domain controllers, Veeam does use snapshots but I believe it has the abililty to put the DCs into the permissive state which allows them to come back online without disruption.

Edited November 12, 2013 by Jamo

[mrbios]

I would say 9 DC's is quite a lot! 2 or 3 is ideal for a school I would have thought. Mainly for resiliency. Unless you have a multi site (ie across WAN connections) having DC's in different buildings/subnets isn't a requirement. On the other hand it won't hurt, just not sure it would provide any benefit.

.

 

Aye like i say it's leftover from pre-virtualisation when we had a DC per building/client based subnet (used to have a physical server in each building back then, that was a pain) i've never bothered to whittle it down to less really. More hassle than it's worth for the minimal fuss it gives me these days .... You can see why i left that for someone else to answer huh?

 

Edit: lol just noticed that was in the article above!!

 

Edited November 12, 2013 by mrbios

[twin--turbo]

We have 4 DC's 1 physical and 1 virtual on either side of the wan.

 

Rob

[tj2419]

How many user accounts, how many concurrent log ons. What is the state of the surrounding network infrastructure.

 

We have around 1200-1300 user accounts, concurrent logons could be reaching 300-400 if all IT rooms were in use at the same time.

 

How many VMs do you expect to be running? and what heavy duty VMs will you be running (SQL for sims, fms etc for one) what about exchange, SCCM etc?

 

Plan is to have VM's for SCCM, Spiceworks, XIBO, Moodle (Fairly well used), Website, then the domain controllers (Depending on number), Print server, think thats about it. In the future it would possibly be also having a SIMS SQL and FMS etc from the admin network but that's only if i win

 

Heavy duty ones would be the Moodle VM and the network servers / DC's. We currently have three servers for our curriculum network svr1 (DC, DHCP, DNS), svr2 (DNS, member server) svr3 (DNS, member server). Would you keep the same setup with 3 vm's or consolidate as the user directories would be stored on the SAN? for the extra resilience. How many of you have two SAN's mirroring? incase your SAN goes wrong?

 

We have 4 DC's 1 physical and 1 virtual on either side of the wan.

 

What is the benefit of keeping a physical DC as well instead of having them all virtualised?

[mrbios]

We have 4 DC's 1 physical and 1 virtual on either side of the wan.

 

What is the benefit of keeping a physical DC as well instead of having them all virtualised?

 

If you forget to setup the automatic startup routine after your whole networks been down it can be a bit of a PITA trying to get access again

 

I've had all my DCs virtual for the past 3 years though, so long as you have more than one and on more than one host it's unlikely to be an issue. Just keep some IPs noted down so that you can connect without DNS should you ever have the occasion arise

 

So would i be right in thinking you're looking at around 10 VMs? plan for 15 in that case (Trust me when you first virtualise you'll suddenly realise there's so much you can setup in an instant that you'll start wanting new things haha) I'd say that two hosts would suffice, but for some reason part of me wants to say 3 even though you wouldn't ever max them out.....on the brightside if you go VMware then you only need to pay for vCenter server foundation rather than standard (You could buy the vSphere essentials plus kit, which gives you 6 CPU licenses to cover up to 3 hosts and vcenter foundation) VMware Europe Official Online Store - VMware vSphere Essentials Kit obviously that's assuming you go down the path of VMware.

[tj2419]

 

So would i be right in thinking you're looking at around 10 VMs? plan for 15 in that case (Trust me when you first virtualise you'll suddenly realise there's so much you can setup in an instant that you'll start wanting new things haha) I'd say that two hosts would suffice, but for some reason part of me wants to say 3 even though you wouldn't ever max them out.

 

Very true. We started of virtualising our moodle install on Xen server and now already have 3 VM's with the spiceworks and XIBO

 

We currently have three servers for our curriculum network svr1 (DC, DHCP, DNS), svr2 (DNS, member server) svr3 (DNS, member server). Would you keep the same setup with 3 vm's or consolidate as the user directories would be stored on the SAN? for the extra resilience. How many of you have two SAN's mirroring? incase your SAN goes wrong?

 

Thanks for all the help and advice a lot to take in but finding it very interesting

[mrbios]

Very true. We started of virtualising our moodle install on Xen server and now already have 3 VM's with the spiceworks and XIBO

 

We currently have three servers for our curriculum network svr1 (DC, DHCP, DNS), svr2 (DNS, member server) svr3 (DNS, member server). Would you keep the same setup with 3 vm's or consolidate as the user directories would be stored on the SAN? for the extra resilience. How many of you have two SAN's mirroring? incase your SAN goes wrong?

 

Thanks for all the help and advice a lot to take in but finding it very interesting

 

What do svr2 and svr3 actually do exactly? (not sure what's involved in being a member server) I think you could just consolidate those 3 into one, then add an additional DC doing dns, dhcp (even if only for failover) too so that you have one on each host. Seems the best way to go to be honest. I reckon you could reuse the hardware from one of these if you wanted to have a physical DC for "just in case" purposes. Some people would, some people wouldn't, up to you really.

 

Rather than mirroring the SAN using the various tools and features SANs can provide to do it the cheaper alternative is to do D2D2T backups and have a really cheap but decent sized RAID6 storage SAN in a separate location to your server room and have it do incremental backups every night and then backup to tape. In a pinch you could commission the slow SAN to take over if the main one died. Performance wouldn't be great but obviously you'd only be looking to use it for a maximum of 1 day anyway. It's a tricky one though, others may give you different advice to this but that's the route I'd look at personally.

[tj2419]

What do svr2 and svr3 actually do exactly? (not sure what's involved in being a member server) I think you could just consolidate those 3 into one, then add an additional DC doing dns, dhcp (even if only for failover) too so that you have one on each host. Seems the best way to go to be honest. I reckon you could reuse the hardware from one of these if you wanted to have a physical DC for "just in case" purposes. Some people would, some people wouldn't, up to you really.

 

Rather than mirroring the SAN using the various tools and features SANs can provide to do it the cheaper alternative is to do D2D2T backups and have a really cheap but decent sized RAID6 storage SAN in a separate location to your server room and have it do incremental backups every night and then backup to tape. In a pinch you could commission the slow SAN to take over if the main one died. Performance wouldn't be great but obviously you'd only be looking to use it for a maximum of 1 day anyway. It's a tricky one though, others may give you different advice to this but that's the route I'd look at personally.

 

Just had a look and svr1, 2,3 are all acting as DC's all running DNS with just svr 1 running DHCP.

 

Possible Setup

I think i would (money permitting) go for 3 hosts, 1 fast SAN, 1 slow SAN. Setup with 3 VM's running as DC's. The additional VM's (Spiceworks, print server etc). Have it set up to replicate across the three hosts incase of a failure of one of them. For the replication incase a host fails i take it the file directories and shared drives need to be stored on the SAN so all the hosts can access it?

 

We already have a pretty good backup system hardware wise with two HP Proliant DL180 G6 servers Xeon E5520 @ 2.27Ghz (8CPUs) and a HP autoloader running backup exec at the min but hopefully change that to veeam. Each with 16TB storage on them (8 * 2TB drives).

 

So am i right in thinking that

 

• As users login and connect to the VM's they are automatically balanced across the three hosts to help with performance?
  
• We can remote onto a particular VM's IP and make changes and that is replicated across the hosts immediatly?
  
• If configured correctly a host could die and users would automatically be redirected to the other two hosts to continue work?
  
• Would you connect the three hosts up to the core switch directly? Have a separate switch linking the Hosts to the SAN for extra speed?
  

 

Thanks

Edited November 14, 2013 by tj2419
Correction

[mrbios]

Just had a look and svr1, 2,3 are all acting as DC's all running DNS with just svr 1 running DHCP.

 

Possible Setup

I think i would (money permitting) go for 3 hosts, 1 fast SAN, 1 slow SAN. Setup with 3 VM's running as DC's. The additional VM's (Spiceworks, print server etc). Have it set up to replicate across the three hosts incase of a failure of one of them. For the replication incase a host fails i take it the file directories and shared drives need to be stored on the SAN so all the hosts can access it?

 

We already have a pretty good backup system hardware wise with two HP Proliant DL180 G6 servers Xeon E5520 @ 2.27Ghz (8CPUs) and a HP autoloader running backup exec at the min but hopefully change that to veeam. Each with 16TB storage on them (8 * 2TB drives).

 

So am i right in thinking that

 

• As users login and connect to the VM's they are automatically balanced across the three hosts to help with performance?
  
• We can remote onto a particular VM's IP and make changes and that is replicated across the hosts immediatly?
  
• If configured correctly a host could die and users would automatically be redirected to the other two hosts to continue work?
  
• Would you connect the three hosts and SAN up to the core switch directly? Have a separate switch linking the Hosts to the SAN for extra speed?
  

 

Thanks

 

I'm going to just play on the assumption of using VMware here as it's the one I'm used to, but with 3 VMware hosts you'd also have a vcenter server (you can make this a VM if you wish, there's even a virtual appliance for it) you can then create a high availability cluster containing the 3 hosts. All 3 hosts would share the same SAN storage so moving machines between the hosts (while running) is as simple as dragging and dropping or right clicking and migrating from one host to another, and it just depends on how much ram is assigned to each VM as to how long it takes to migrate (even my biggest VM with 24gb ram only takes 1-2 minutes at max) and that's all it takes to get a VM running on a different host, so you can balance these out yourself quite easily. There's also very granular performance graphs and event warnings for high latency etc so you can adjust it pretty easily, the VMs don't auto balance themselves based on performance BUT if one host fails with 5 running VMs on them, the cluster will automatically bring those 5 VMs back up on a different host. So you get a couple of minutes down time on those VMs (or less, VMs boot really really fast) but the system automatically brings them back up for you.

 

I'd connect up the 3 hosts directly to the core, but then all the iSCSI traffic from hosts to SAN (assuming you went for iSCSI) i'd have on a separate switch, and using separate ports on the host (ideally as a separate vlan)....still connected to the core as a center point for the vlan routing, but the traffic just wouldn't go out that way.