HP EVA P6550 HP P6300/P6500 EVA User Guide (5697-2486, September 2013) - Page 39

When creating a virtual disk, one controller is selected to manage the virtual disk. Only this managing controller can issue I/Os to a virtual disk in response to a host read or write request. If a read I/O request arrives on the non-managing controller, the read request must be transferred to the managing controller for servicing. The managing controller issues the I/O request, caches the read data, and mirrors that data to the cache on the non-managing controller, which then transfers the read data to the host. Because this type of transaction, called a proxy read, requires additional overhead, it provides less than optimal performance. (There is little impact on a write request because all writes are mirrored in both controllers' caches for fault protection.) With implicit LUN transition, when the array detects that a majority of read requests for a virtual disk are proxy reads, the array transitions management of the virtual disk to the non-managing controller. This improves performance because the controller receiving most of the read requests becomes the managing controller, reducing proxy read overhead for subsequent I/Os. Implicit LUN transition is disabled for all members of an HP P6000 Continuous Access DR group. Because HP P6000 Continuous Access requires that all members of a DR group be managed by the same controller, it would be necessary to move all members of the DR group if excessive proxy reads were detected on any virtual disk in the group. This would impact performance and create a proxy read situation for the other virtual disks in the DR group. Not implementing implicit LUN transition on a DR group may cause a virtual disk in the DR group to have excessive proxy reads. Recovery CD HP does not ship the recovery CD with the HP P6350/P6550 EVA. You can download the image from the HP Software Depot at the following URL and burn a CD, if needed: http://www.software.hp.com Adding disk drives to the storage system As your storage requirements grow, you may be adding disk drives to your storage system. Adding new disk drives is the easiest way to increase the storage capacity of the storage system. Disk drives can be added online without impacting storage system operation. Consider the following best practices to improve availability when adding disks to an array: • Set the add disk option to manual. • Add disks one at a time, waiting a minimum of 60 seconds between disks. • Distribute disks vertically and as evenly as possible to all the disk enclosures. • Unless otherwise indicated, use the SET DISK_GROUP command in the HP Storage System Scripting Utility to add new disks to existing disk groups. • Add disks in groups of eight. • For growing existing applications, if the operating system supports virtual disk growth, increase virtual disk size. Otherwise, use a software volume manager to add new virtual disks to applications. See the HP Disk Drive Replacement Instructions for the steps to add a disk drive. See "Replacement instructions" (page 85) for a link to this document. Handling fiber optic cables This section provides protection methods for fiber optic connectors. Contamination of the fiber optic connectors on either a transceiver or a cable connector can impede the transmission of data. Therefore, protecting the connector tips against contamination or damage is imperative. The tips can be contaminated by touching them, by dust, or by debris. They can be damaged when dropped. To protect the connectors against contamination or damage, use the dust covers or dust caps provided by the manufacturer. These covers are removed during installation, and should be installed whenever the transceivers or cables are disconnected. Operating tips and information 39