Dell PowerVault MD3000, Hardware Owner'S Manual

Page: 34 / 102

34
Using Your RAID Enclosure
Cycle Time
The media verification operation runs only on selected disk groups, independent of other disk groups.
Cycle time is how long it takes to complete verification of the metadata region of the disk group and all
virtual disks in the disk group for which media verification is configured. The next cycle for a disk group
starts automatically when the current cycle completes. You can set the cycle time for a media verification
operation between 1 and 30 days. The firmware throttles the media verification I/O accesses to disks
based on the cycle time.
The RAID controller module tracks the cycle for each disk group independent of other disk groups on
the controller and creates a checkpoint. If the media verification operation on a disk group is preempted
or blocked by another operation on the disk group, the firmware resumes after the current cycle. If the
media verification process on a disk group is stopped due to a RAID controller module restart, the
firmware resumes the process from the last checkpoint.
Virtual Disk Operations Limit
The maximum number of active, concurrent virtual disk processes per controller is four. This limit is
applied to the following virtual disk processes: background initialization, foreground initialization,
consistency check, rebuild, and copy back.
If a redundant controller fails with existing virtual disk processes, the processes on the failed controller
are transferred to the peer controller. A transferred process is placed in a suspended state if there are four
active processes on the peer controller. The suspended processes are resumed on the peer controller when
the number of active processes falls below four.
Disk Group Operations
RAID Level Migration
Over time, you may determine that characteristics of the initial RAID level you set initially are no longer
appropriate for your enterprise. For example, you can add fault-tolerant characteristics to a stripe set
(RAID 0) by converting it to a RAID 5 set. Select the virtual disk that you want to change and select the
type of RAID level to which you want to migrate. MD Storage Manager provides information about
RAID attributes to assist you in selecting the appropriate level. You can perform a RAID level migration
while the system is still running and without rebooting, which maintains data availability.
Segment Size Migration
Segment size refers to the amount of data (in kilobytes) that the RAID controller module writes on a
single physical disk in a virtual disk before writing data on the next physical disk. Valid values for the
segment size are 8, 16, 32, 64, 128, 256, and 512 KB.
Dynamic segment size migration enables the segment size of a given virtual disk to be changed. A
default segment size was set when the virtual disk was created, based on such factors as the RAID level
and expected usage. You can change the default value if actual usage does not match your needs.