What is the crowd's opinion of
OpenStack?
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➔ OpenStack website
By popularity online, this Service is:
2 reviews of this app found across the web:
http;//Openstack.org is the starting place. They recently put up a Architecture Design guide. Icehouse is much more stable then previous releases.
Redhat (& CentOS) has a tool called packstack that can build an allinone and then add compute nodes. Redhat's site is http://openstack.redhat.com
Canonical (ubuntu) and Mirantis, Rackspace and Piston are other big and players and have deployment tools.
Since you're doing KVM, your VMs won't need to be converted. Openstack supports other hypervisors, but KVM is the main one. Some commercial clouds use Xen.
As others have said, I'd stay away from the flat model.
Not raid.
We don't know exactly how Amazon S3 works on the back end, but OpenStack does not use raid. It is a non-traditional file system on top of inexpensive consumer disks, in inexpensive consumer boxes. Redundancy is tunable and is handled by the object tracking system.