[CentOS] kvm cluster w/ c6

[Digimer]

On 20/10/13 02:22, John R Pierce wrote:
> In our development lab, I am installing 4 new servers, that I want to 
> use for hosting KVM.   each server will have its own direct attached 
> raid.   I'd love to be able to 'pool' this storage, but over gigE, I 
> probably shouldn't even try.

I've build DRBD-backed shared storage using 1 Gbit network for
replication for years and the network has not been an issue. So long as
your apps can work with ~110 MB/sec max throughput, you're fine.

Latency is not effected because the average seek time of a platter, even
15krpm SAS drives, it higher than the network latency (assuming decent
equipment).

> most of the VM's will be running CentOS 5 and 6,  some of the VM's will 
> be postgresql database dev/test servers, others will be running java 
> messaging workloads, and various test jobs.
> 
> to date, my experience with KVM is bringing up one c6 VM on a c6 host, 
> manually w/ virt-install and virsh...
> 
> stupid questions ...
> 
> whats the best storage setup for KVM when using direct attached raid?  
> surely using disk image files on a parent ext4/xfs file system isn't the 
> best performance?    Should I use host lvm logical volumes as guest 
> vdisks?   we're going to be running various database servers in dev/test 
> and wanting at least one or another at a time to really be able to get 
> some serious iops.

What makes the most difference is not the RAID configuration but having
batery-backed (or flash-backed) write caching. With multiple VMs having
high disk IO, it will get random in a hurry. The caching allows for
keeping the systems responsive even under these highly random writes.

As for the storage type; I use clustered LVM (with DRBD as the PVs) and
give each VM a dedicated LV, as you mentioned above. This takes the FS
overhead out of the equation.

> its virt-manager worth using, or is it too simplistic/incomplete ?

I use it from my laptop, via an ssh tunnel, to the hosts all the time. I
treat it as a "remote KVM" switch as it gives me access to the VMs
regardless of their network state. I don't use it for anything else.

> will virt-manager or some other tool 'unify' management of these 4 VM 
> hosts, or will it be pretty much, me-the-admin keeps track of what vm is 
> on what host and runs the right virt-manager and manages it all fairly 
> manually?

Depends what you mean by "manage" it. You can use 'virt-manager' on your
main computer to connect to the four hosts (and even set them to
auto-connect on start). From there, it's trivial to boot/connect/shut
down the guests.

If you're looking for high-availability of your VMs (setting up your
servers in pairs), this might be of interest;

https://alteeve.ca/w/2-Node_Red_Hat_KVM_Cluster_Tutorial

-- 
Digimer
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