Dell PowerVault MD3620i Owner's Manual - Page 46

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, 16, 32, 64, 128, 256, and 512 KBs. 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. 46 Planning: MD3600i Series Storage Array Terms and Concepts