after the current cycle. If the media verification process on a disk group is stopped due to a RAID controller module restart, the storage
array resumes the process from the last checkpoint.
Virtual disk operations limit
The maximum number of active, concurrent virtual disk processes per RAID controller module installed in the storage array is four. This limit
is applied to the following virtual disk processes:
•
Background initialization
•
Foreground initialization
•
Consistency check
•
Rebuild
•
Copy back
If a redundant RAID controller module 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
You can migrate from one RAID level to another depending on your requirements. For example, fault-tolerant characteristics can be added
to a stripe set (RAID 0) by converting it to a RAID 5 set. The MD Storage Manager provides information about RAID attributes to assist you
in selecting the appropriate RAID 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 storage array writes on a physical disk in a virtual disk before writing data
on the next physical disk. Valid values for the segment size are 8 KB, 16 KB, 32 KB, 64 KB, 128 KB, and 256 KB.
Dynamic segment size migration enables the segment size of a given virtual disk to be changed. A default segment size is set when the
virtual disk is created, based on such factors as the RAID level and expected usage. You can change the default value if segment size usage
does not match your needs.
When considering a segment size change, two scenarios illustrate different approaches to the limitations:
•
If I/O activity stretches beyond the segment size, you can increase it to reduce the number of disks required for a single I/O. Using a
single physical disk for a single request frees disks to service other requests, especially when you have multiple users accessing a
database or storage environment.
•
If you use the virtual disk in a single-user, large I/O environment (such as for multimedia application storage), performance can be
optimized when a single I/O request is serviced with a single data stripe (the segment size multiplied by the number of physical disks in
the disk group used for data storage). In this case, multiple disks are used for the same request, but each disk is only accessed once.
Virtual disk capacity expansion
When you configure a virtual disk, you select a capacity based on the amount of data you expect to store. However, you may need to
increase the virtual disk capacity for a standard virtual disk by adding free capacity to the disk group. This creates more unused space for
new virtual disks or to expand existing virtual disks.
About your MD Series storage array
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