46 Planning: MD3200 Series Storage Array Terms and ConceptsDynamic segment size migration enables the segment size of a given virtualdisk to be changed. A default segment size is set when the virtual disk iscreated, based on such factors as the RAID level and expected usage. You canchange the default value (128 KB) if segment size usage does not match yourneeds.When considering a segment-size change, two scenarios illustrate differentapproaches to the limitations:• If I/O activity stretches beyond the segment size, you can increase it toreduce the number of disks required for a single I/O. Using a single physicaldisk for a single request frees disks to service other requests, especiallywhen 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 asfor multimedia application storage), performance can be optimized whena single I/O request is serviced with a single data stripe (the segment sizemultiplied by the number of physical disks in the disk group used for datastorage). In this case, multiple disks are used for the same request, buteach disk is only accessed once.Virtual Disk Capacity ExpansionWhen you configure a virtual disk, you select a capacity based on the amountof data you expect to store. However, you may need to increase the virtual diskcapacity 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 existingvirtual disks.Disk Group ExpansionBecause the storage array supports hot pluggable physical disks, you can addtwo physical disks at a time for each disk group while the storage arrayremains online. Data remains accessible on virtual disk groups, virtual disks,and physical disks throughout the operation. The data and increased unusedfree space are dynamically redistributed across the disk group. RAIDcharacteristics are also reapplied to the disk group as a whole.
