Server Cluster Suitable for School?

[fiza]

I've heard alot about having servers in a cluster but is it too much for a school environment? We have 1000 students and 150 staff (Secondary School) . Currently have 6 servers but half of these are due for replacement now and the rest in a year or 2. I have seen schools with VM hosts in a cluster attached to a SAN. Is this overkill or something that we should be looking at?

[Duke]

I think clustering in the normal sense of the word is probably overkill for a school - you usually don't need the level of uptime provided by services spanned across multiple servers with fault tolerance. I suppose the exception might be Exchange and SQL if you're really dependent on them, as Microsoft have designed them to be fairly easy to cluster.

 

A VMware cluster is fairly sensible though if you're going the virtualisation route. If you're getting a decent hypervisor and have more than one host then you'll be doing clustering anyway. VMware will give you failover (a host dies, the VMs on it are moved to a different host and powered back up) and/or fault tolerance (two instances of a VM are run across two hosts in lockstep, if one dies then the other instantly takes over).

 

Chris

[fiza]

A VMware cluster is fairly sensible though if you're going the virtualisation route. If you're getting a decent hypervisor and have more than one host then you'll be doing clustering anyway. VMware will give you failover (a host dies, the VMs on it are moved to a different host and powered back up) and/or fault tolerance (two instances of a VM are run across two hosts in lockstep, if one dies then the other instantly takes over).

 

Chris

 

Would this apply in a Hyper-V environment? 2 Hyper-V hosts with an attached SAN? Does Hyper-V offer the same failover scenario?

[CyberNerd]

You'd need a cluster aware filesystem such as GFS2.

I wouldn't think it overkill because I'd quite like to be able to restart (virtual) machines and not loose services, so I can certainly see use for clustering in schools.

[Duke]

Would this apply in a Hyper-V environment? 2 Hyper-V hosts with an attached SAN? Does Hyper-V offer the same failover scenario?

 

I'm not as familiar with Hyper-V as VMware, but yes, the basic clustering of hosts applies. I don't think Hyper-V offers fault tolerance (i.e. a server instantly failing over to another machine with no downtime), but I think Microsoft were working on it and it's not that practical a feature anyway, even in VMware.

 

Basically, you have n+1 hosts, where n is the number of hosts needed to run all your virtual machines. No good having two hosts running at 80% capacity, because when one fails you're suddenly trying to run one host at 160% capacity, thus n+1. Have some shared storage so your machines can move between hosts, and you're all good.

[Gardinho]

I would agree with @Duke regarding VMWare clustering.

 

If the money is available, than I wouldn't consider it overkill. In fact, I would consider it good practise. Since we installed our VMware infrastructure we have had 100% uptime.

 

I suppose it depends on your network and the priorities for investment.

[CyberNerd]

vmware clusters are not the same as server clusters in this context.

If you restart a virtual host then the service remains up but if you reboot or shutdown a virtual server you still loose the service. If the virtual servers are clustered the service remains up if one of the hosts are down. Moreover, clusters allow two or more servers to answer requests, providing more processing power and bandwidth.

[TronXP]

We have been clustering in our school for 6 years or so, I had file and print services clustered on Netware 6.5, then when we moved to Server 2008R2 we continued with it. Clustering of services is brilliant for more than one reason. First of all, if a server goes down or has an issue, then your services remain. But the other thing especially for us, is that we can move services to another server then perform maintenance on hardware during office hours without affecting our service. Our school doesn't like paying us to come in weekends or late nights so this for us makes our life a lot easier.

 

Now I am talking about clustering between services between physical servers using MSCS, not using any virtual as yet

[Gardinho]

vmware clusters are not the same as server clusters in this context.

If you restart a virtual host then the service remains up but if you reboot or shutdown a virtual server you still loose the service. If the virtual servers are clustered the service remains up if one of the hosts are down. Moreover, clusters allow two or more servers to answer requests, providing more processing power and bandwidth.

 

In what context? The OP asked about VM hosts in a cluster attached to a SAN. Is that not essentially a vmware (or any virtualisation product) cluster?

Edited May 3, 2012 by Gardinho

[CyberNerd]

just saying that it has different meanings. Clustering VMHosts is fairly limited, whereas clustering servers 'in the traditional sense' has much more practical benefits.

[Duke]

just saying that it has different meanings. Clustering VMHosts is fairly limited, whereas clustering servers 'in the traditional sense' has much more practical benefits.

 

Give and take in my option - Some software/services aren't cluster-aware and can't be made to be. In those scenarios VMware fault-tolerance my be your only option for non-interrupted uptime. VMware (or a virtual cluster in general) allows you to have failover and possibly fault-tolerance for all of your servers and services on the network as part of its basic functionality. Application-level clustering like you're talking about is usually much more limited to a specific service and you'll normally need to buy more enterprise-level software licenses to get this functionality.

 

I do agree, however, that if you have a service which needs a very high level of uptime, proper application-aware clustering across multiple hosts is the best way to do it, rather than just relying on VMware.