Selecting Virtual Drive Settings
Keywords: MegaRAID SAS SW UG

> Selecting Virtual Drive Settings

> This section describes the virtual drive settings that you can select when you use the advanced configuration procedure to create virtual drives. You should change these parameters only if you have a specific reason for doing so. It is usually best to leave them at their default settings.

> | Initialization state:

> Initialization prepares the storage medium for use. Specify the initialization status:

> | No Initialization (Default)

> The new configuration is not initialized, and the existing data on the drives is not overwritten.

> | Fast Initialization

> The firmware quickly writes 0s to the first and last 8-MB regions of the new virtual drive and then completes the initialization in the background. This allows you to start writing data to the virtual drive immediately.

> | Full Initialization

> A complete initialization is done on the new configuration. You cannot write data to the new virtual drive until the initialization is complete. This process can take a long time if the drives are large.

> NOTE BGI is supported only for RAID 5 and RAID 6 and not for any other RAID levels. New RAID 5 virtual drives require at least five drives for a background initialization to start. New RAID 6 virtual drives require at least seven drives for a background initialization to start. If there are fewer drives, the background initialization does not start.

> | Strip size

> Strip sizes of 8 KB, 16 KB, 32 KB, 64 KB, 128 KB, 256 KB, 512 KB, and 1024 KB are supported. The default is 64 KB. For more information, see the striping entry in the Glossary.

> | Read policy

> Specify the read policy for this virtual drive:

> | Always read ahead

> Read ahead capability allows the controller to read sequentially ahead of requested data and to store the additional data in cache memory, anticipating that the data will be needed soon. This process speeds up reads for sequential data, but little improvement occurs when accessing random data.

> | No read ahead (Default)

> Disables the read ahead capability.

> | Write policy

> Specify the write policy for this virtual drive:

> | Write Through

> In this mode, the controller sends a data transfer completion signal to the host when the drive subsystem has received all of the data in a transaction. This option eliminates the risk of losing cached data in case of a power failure.

> | Always Write Back

> In this mode, the controller sends a data transfer completion signal to the host when the controller cache receives all the data in a transaction. If you select the Always Write Back policy and the battery is absent, the firmware is forced to use the Write Back policy.

> | Write Back (Default)

> In this mode, the controller sends a data transfer completion signal to the host when the controller cache receives all of the data in a transaction. If you select the Write Back policy and the battery is absent, the firmware disables the Write Back policy and defaults to the Write Through policy. This option provides a good balance between data protection and performance.

> NOTE 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 current write policy switches to Write Through, which provides better data protection.

> | I/O policy

> The I/O policy applies to reads on a specific virtual drive. It does not affect the read ahead cache.

> | Cached IO

> In this mode, all reads are buffered in cache memory.

> | Direct IO (Default)

> 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.

> Cached IO provides faster processing, and Direct IO makes sure that the cache and the host contain the same data.

> | Access policy

> Select the type of data access that is allowed for this virtual drive.

> | Read/Write (Default)

> Allow read/write access. This setting is the default value.

> | Read Only

> Allow read-only access.

> | Blocked

> Do not allow access.

> | Disk cache policy

> Select a cache setting for this drive:

> | Enabled

> Enable the disk cache.

> | Disabled (Default)

> Disable the disk cache.

> | Unchanged

> Leave the current disk cache policy unchanged.

DB09000202-21, Rev 2.2, July 2015
Copyright© 2015 by Avago Technologies. All rights reserved.