Take care when adding, removing, and resizing LUNs as it may require a physical server reboot. Do not resize LUNs that are used as part of Logical disks; instead, create a new LUN and add it to the disk group.

Avoid remapping LUNs as this can cause data corruption since the targets have been switched outside of the server. The Linux SCSI layer does not support dynamic remapping of LUNs from the storage array.

Test your configuration, especially fail over, in a test environment before rolling into production. If your (SAN) array firmware is at a different release number than we have tested, confirm whether there are any differences. You may need to make changes to the multipath configuration files of Oracle VM Server.

Plan the size and type of storage that you are using by workload. For example:

If using storage server features such as cloning and snapshots, use raw disks.

While it may be tempting to create a very large LUN when using logical disks, this can be detrimental to performance as each virtual machine queues I/Os to the same disks. Oracle recommend that storage repositories do not exceed 2TB.

Be sure to leave some disk space available to create smaller storage entities of, at least, 12GB each to use as server pool file systems. The server pool file system is used to hold the server pool and cluster data, and is also used for cluster heartbeating. You create space for server pool file systems the same way as you create storage entities for storage repositories. For more information about the use and management of clusters and server pools, see Chapter 6, Managing Server Pools and Oracle VM Servers.

Place server pool file systems on a separate NFS server or use a small LUN, if possible. The OCFS2 heartbeating function can be disturbed by I/O-intensive operations on the same physical storage. For example: importing a template or cloning a VM in a storage repository on the same NFS server where the server pool file system resides may cause a time-out in the heartbeat communication, which in turn leads to server fencing and reboot. To avoid unwanted rebooting, it is recommended that you choose a server pool file system location with sufficient and stable I/O bandwidth.

Disable read and write caching on the underlying disk systems to guarantee I/O synchronization. Caching may result in data loss if the Oracle VM Server or a virtual machine fails abruptly. To disable write caching, change the applicable settings in the RAID controller BIOS. Alternatively, use the sg_wr_mode command or use the SCSI disk class directly: echo "write through" > /sys/class/scsi_disk/scsi-device-id/cache_type.