Administrator Guide

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.

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

If a redundant RAID controller module fails with an existing disk group process, the process on the failed controller is

transferred to the peer controller. A transferred process is placed in a suspended state if there is an active disk group