Users Guide

Conditions under which forced write-back with no battery is employed

CAUTION: It is recommended that you use a power backup system when forcing write-back to ensure there is no

loss of data if the system suddenly loses power.

Write-back mode is available when you select force write-back with no battery. When forced write-back mode is selected, the

virtual disk is in write-back mode even if the battery is not present.

Virtual disk read cache policy

The read policy of a virtual disk determines how the controller handles reads to that virtual disk.

Table 5. Read policies

Feature Description

Read ahead Allows the controller to read sequentially ahead of requested data and to store the additional data in

cache memory, anticipating that the data is required soon. This speeds up reads for sequential data,

but there is slight improvement when accessing random data.

No read ahead Disables the read ahead capability.

NOTE: Adaptive read ahead is no longer supported. Selecting adaptive read ahead is equivalent to selecting the read ahead

option.

Virtual disk migration

The PERC 11 series supports migration of virtual disks from one controller to another without taking the target controller offline.

The controller can import RAID virtual disks in optimal, degraded, or partially degraded states. You cannot import a virtual disk

that is offline. When a controller detects a configured physical disk, it marks the physical disk as foreign, and generates an alert

indicating that a foreign disk was detected.

Disk migration pointers:

● Supports migration of virtual disks from PERC H345, H740P, H745, H745P MX, and H840 to the PERC 11 series except for

H345.

● Supports migration of volumes created within the PERC 11 series.

● Does not support migration from the PERC 11 series to PERC H345, H740P, H745, H745P MX, and H840.

● Does not support migration from PERC H330, H730, and H830 to the PERC 11 series.

NOTE: The source controller must be offline prior to performing the disk migration.

NOTE: Importing non–RAID drives and uneven span RAID 10 virtual disks from PERC 9 to PERC 11 is not supported.

NOTE: Disks cannot be migrated to older generations of PERC cards.

NOTE: Importing secured virtual disks is supported as long as the appropriate local key management (LKM) is supplied or

configured.

NOTE: Virtual disk migration from PERC H740P, H745P, H745, H840 to H345 is not supported.

CAUTION: Do not attempt disk migration during RLM or online capacity expansion (OCE), this causes loss of the

virtual disk.

Virtual disk initialization

PERC 11 series controllers support two types of virtual disk initialization:

● Full initialization

● Fast initialization

Features of PowerEdge RAID Controller 11