CVM vs CFS difference

[Ivan Rodriguez Sanchez]

Hi all,

I'm reading documentation about SG Cluster Storage Management Suite, because I have to configure a multi node cluster with CFS. After reading lots of docs, I don't know yet what is the difference between CFS and CVM, and when you have to use CFS with CVM and when CFS without CVM.

Thanks a lot!

[Matti_Kurkela · Accepted solution]

CFS = Cluster File System. In case of HP-UX, this means an advanced version of VxFS with the cluster support enabled. It provides the ability to mount the filesystem on multiple nodes simultaneously.
(If you try to do it without a proper CFS, the OS will not stop you but your filesystem will get massively corrupted very rapidly because the nodes won't coordinate their actions on the filesystem.)

CVM = Cluster Volume Manager. In case of HP-UX, this means VxVM with the cluster support enabled. It allows you to manage the disk group while it's active on multiple nodes. (Regular HP-UX LVM can allow a VG to be activated in shared mode on multiple nodes, but the VG cannot be e.g. extended or migrated to another disk while it's in shared mode.)

The Storage Management Suite includes the appropriate licenses for both of the above. I understand the recommended practice is to use CVM whenever you're using CFS (at least on older versions of CFS, it was even a requirement; I'm not sure about the latest version).

MK

[John Bigg]

CFS is a cluster file system. CVM is a cluster volume manager.

CFS requires CVM but not vice versa. If you want to access shared but raw volumes all you would need is CVM. But if you want to share a filesystem, you need to sit this on top of a shared volume.

A cluster file system is a shared filesystem which sits on top of a shared volume.