Storage Requirements

Be aware of the following limitations with SAN and NAS:

• Ensure that Orchestrator is not running on virtual machines if your storage is based on SAN Fiber Channel technology, since virtual machines typically do not support SAN Fiber Channel storage.
• A SAN storage requires a cluster file system (for example, GFS) for our HA solution to work. A block level storage access will not work; only a file level storage access is suitable. Files must be visible from both nodes concurrently. If a file is changed from one node, the other node must be able to immediately incorporate the changes. For example, a storage mount based on raw device mapping (RDM) is at the block level. RDM is a VMware server virtualization environment that enables storage to be directly connected to a virtual machine from the SAN. This will work, as file updates on one node are not visible to the other node until the shared storage is remounted.
• A NAS storage based on NFS requires NFS Version 4. A solution based on NFS Version 3 may cause problems, because NFS3 does not automatically release the locks held by a client. This is critical for MySQL, where only one node at a time may write to the shared disk; the Orchestrator MySQL version does not support locking on concurrent writes. With NFS3, if the active node that is running MySQL goes down, the passive node is unlikely to be able to start MySQL when it takes over, because some MySQL files may still be locked on the shared storage. With NFS4 technology, all locks associated with a TCP session that times out will be automatically released, making MySQL automatic failover possible. A NAS storage based on CIFS (for example, Samba) will work, because there are no locking issues.