Users Guide

Table 7. Drive state/operation (continued)
Drive state/operation Unconfigured
slot
Slot configured in VD
● Original drive data lost
Insert locked drive into the system (non-unlockable) Foreign locked Foreign locked
Physical disk hot swapping
Hot swapping is the manual replacement of a disk while the PERC 11 series cards are online and performing their normal
functions. The following requirements must be met before hot swapping a physical disk:
● The system backplane or enclosure must support hot swapping for the PERC 11 series cards.
● The replacement disk must be of the same protocol and disk technology. For example, only a SAS hard drive can replace a
SAS hard drive and only a NVMe drive can replace a NVMe drive.
Using replace member and revertible hot spares
The replace member functionality allows a previously commissioned hot spare to revert to a usable hot spare. When a disk failure
occurs within a virtual disk, an assigned hot spare, dedicated, or global, is commissioned and begins rebuilding until the virtual
disk is optimal. After the failed disk is replaced in the same slot and the rebuild to the hot spare is complete, the controller
automatically starts to copy data from the commissioned hot spare to the newly inserted disk. After the data is copied, the
new disk is a part of the virtual disk and the hot spare is reverted to being a ready hot spare. This allows hot spares to
remain in specific enclosure slots. While the controller is reverting the hot spare, the virtual disk remains optimal. The controller
automatically reverts a hot spare only if the failed disk is replaced with a new disk in the same slot. If the new disk is not placed
in the same slot, a manual replace member operation can be used to revert a previously commissioned hot spare.
NOTE:
A replace member operation typically causes a temporary impact to disk performance. Once the operation
completes, performance returns to normal.
Controller cache
The PERC 11 series of cards contain local DRAM on the controllers. This DRAM can cache I/O operations for Write Back, Read
Ahead virtual disks to improve the performance.
NOTE:
Virtual disks consisting of SSDs may not see a difference in performance using controller cache and may benefit by
Fastpath.
I/O workload that is slow to HDDs, such as random 512 B and 4 kB, may take some time to flush cached data. Cache is flushed
periodically but for configuration changes or system shutdown, the cache is required to be flushed before the operation can be
completed. It can take several minutes to flush cache for some workloads depending on the speed of the HDDs and the amount
of data in the cache.
The following operations require a complete cache flush:
● Configuration changes (add or delete VDs, VD cache setting changes, foreign configuration scan, and import)
● System reboot or shutdown
● Abrupt power loss causing cache preservation
NOTE:
The iDRAC or OpenManage periodically scans for the foreign configurations when the foreign disks are present.
This action degrades the performance. If a foreign disk is present, it is recommended that you import, clear, or remove the
foreign disk to prevent an impact on the performance.
Controller cache preservation
The controller is capable of preserving its cache in the event of a system power outage or improper system shutdown. The
PERC 11 series controller is attached to a battery backup unit (BBU) that provides backup power during system power loss to
preserve the controller's cache data.
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Features of PowerEdge RAID Controller 11