Administrator Guide

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.
For more information about virtual disk capacity expansion, see Virtual disk expansion on page 81.
Disk group expansion
Because the storage array supports hot-swappable physical disks, you can add two physical disks at a time for each disk group while the
storage array remains online. Data remains accessible on virtual disk groups, virtual disks, and physical disks throughout the operation. The
data and increased unused free space are dynamically redistributed across the disk group. RAID characteristics are also reapplied to the
disk group as a whole.
Disk group defragmentation
Defragmenting consolidates the free capacity in the disk group into one contiguous area. Defragmentation does not change the way in
which the data is stored on the virtual disks.
Disk group operations limit
The maximum number of active, concurrent disk group processes per installed RAID controller module is one. This limit is applied to the
following disk group processes:
• Virtual disk RAID level migration
• Segment size migration
• Virtual disk capacity expansion
• Disk group expansion
• Disk group defragmentation
About your MD Series storage array
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