Avago Technologies Syncro 9361-8i - Manual (Page 14)

Avago Technologies
- 14 -
Syncro CS 9361-8i and Syncro CS 9380-8e Solution User Guide 
October 2014
Chapter 2: Creating the Cluster
Creating Virtual Drives on the Controller Nodes
15. Define hot spare disks for the VDs to maximize the level of data protection.
NOTE The Syncro CS 9361-8i and Syncro CS 9380-8e solution supports global
hot spares and dedicated hot spares. Global hot spares are global for
the cluster, not for a controller.
16. When all VDs are configured, reboot both systems as a cluster.
2.1.2 Selecting Additional Virtual Drive Properties
This section describes the following additional virtual drive properties that you can select while you create virtual
drives. Change these parameters only if you have a specific reason for doing so. It is usually best to keep them at their
default settings.
 Strip Size – The strip size is the portion of the stripe that resides on a single virtual drive in the drive group. Strip
sizes of 64 KB, 128 KB, 256 KB, 512 KB, or 1 MB are supported.
 Read Policy – Specify one of the following options to specify the read policy for this virtual drive:
— Normal – Read ahead capability lets the controller read sequentially ahead of requested data and to store
the additional data in cache memory, thereby anticipating that the data will be needed soon. This process
speeds up reads for sequential data, but there is little improvement when the computer accesses random
data.
— Ahead – Disables the read ahead capability.
 Write Policy – Select one of the following options to specify the write policy for this virtual drive
— Write Thru – In this mode, the controller sends a data transfer completion signal to the host when the drive
subsystem has received all the data in a transaction. This option eliminates the risk of losing cached data in
case of a power failure.
— Write Back – In this mode, the controller sends a data transfer completion signal to the host when the
controller cache has received all the data in a transaction.
— Write Back with BBU – In this mode the controller has no BBU or the BBU is bad. If you do not choose this
option, the controller firmware automatically switches to the Write Thru mode if it detects a bad or missing
BBU.
CAUTION The write policy depends on the status of the BBU. If the BBU is not
present, is low, is failed, or is being charged, the virtual drive is still in
the Write Back mode and there is a chance of data loss.
 I/O Policy – The I/O policy applies to reads on a specific virtual drive. It does not affect the read ahead cache.
— Cached – In this mode, all reads are buffered in cache memory. Cached I/O provides faster processing.
— Direct – In this mode, reads are not buffered in cache memory. Data is transferred to the cache and the host
concurrently. If the same data block is read again, it comes from cache memory. Direct I/O makes sure that
the cache and the host contain the same data.
 Disk cache policy – Select a cache setting for this virtual drive:
— Enable – Enable the drive cache.
— Disable – Disable the drive cache.
— Unchanged – Updating the drive cache policy to Unchanged may enable /disable the drive cache based on
the WCE (Write Cache Policy) bit of the save mode page of the drive.
 Initialize – Select to initialize the virtual drive. Initialization prepares the storage medium for use. Fast
initialization will be performed on the virtual drive.
 Configure Hot Spare – Select to configure physical drives as hot spares for the newly created virtual drive.
This option is enabled only if there are additional drives and if they are eligible to be configured as hot spares. This
option is not applicable for RAID 0. If you select this option and after the Virtual drive is created, a dialog appears.
The dialog asks you to choose the physical drives that you want to configure as hot spares.