November 27, 2013 at 9:01 am
Hello
Could someone provide insight on using 2 VMs in a cluster fro SQL Server 2008 R2 (or higher)?
Today, I have 2 physical boxes in an active passive cluster that use shard storage. This gives me HA on the OS & SQL instance.
The capacity planning team wants to have SQL on a VM and boast that SQL can run anywhere - but then we lose the HA we have. (Theirs is a warm manual failover, today we have a hot automatic failover).
I asked if we ciould try clustering 2 VMs and they said OK but I havent heard back and I think I heard Brent Ozar make a comment that clustering 2 VMs wasn't recomended - but I can't find details.
Thanks
Dave
November 27, 2013 at 9:12 am
Clustering the VM's is not hugely different to clustering physical servers.
The issue you may have is that if both VM's are hosted on the same underlying physical hardware and the host goes down then so do both VM's.
Depending on the VM software being used setting up the shared storage can be tricker but technically there is no reason why you can't but it all depends on your business's opinon on what the consider a feasable and cost effective HA solution.
One alternative would be to move to always on with virtual hosts, but it has many drawbacks that you would need to consider first such as replication, additonal storage, would the VM's again be one the same physical hardware etc etc.
MCITP SQL 2005, MCSA SQL 2012
November 28, 2013 at 7:24 am
We have deployed several VM clusters with SQL 2012 on VMWare, and there's some caveats to it. If you want to use shared storage it basically breaks, at least for VMWare, some of its HA capabilities (like VMotion), and I believe that affects all VMs on same Host, making it basically useless for the great HA capabilities built into VMWare.
With a 2 node VM cluster with node majority, failure of 1 node takes the cluster down, so you would need at least 3 nodes to allow for 1 failure. With Windows 2008R2 and up you can also use a shared drive (file share) as Quorum, but that doesn't give you better odds.
Each VM has its own storage attached and using SQL 2012 AlwaysOn you control your HA of SQL while VMWare takes care of the HA of each VM node.
November 29, 2013 at 6:32 am
NJDave (11/27/2013)
HelloCould someone provide insight on using 2 VMs in a cluster fro SQL Server 2008 R2 (or higher)?
Today, I have 2 physical boxes in an active passive cluster that use shard storage. This gives me HA on the OS & SQL instance.
The capacity planning team wants to have SQL on a VM and boast that SQL can run anywhere - but then we lose the HA we have. (Theirs is a warm manual failover, today we have a hot automatic failover).
I asked if we ciould try clustering 2 VMs and they said OK but I havent heard back and I think I heard Brent Ozar make a comment that clustering 2 VMs wasn't recomended - but I can't find details.
Thanks
Dave
Clustering is perfectly viable for VMs however the shared storage required does introduce some limitations. The shared drives need to be attached to the VMWare host as raw volumes and then presented straight to the VMs. Raw device mappings can be harder to manage between the VMWare hosts, this generally puts most people off.
The changes to the cluster quorum types in Windows 2003 SP2 on have significantly improved clustering. The fileshare witness, if needed, should be employed rather than a shared disk. In Windows 2008 clusters you can make advanced configurations by removing votes from certain cluster nodes, ensuring that your ideal cluster uptime is met.
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