Home > Storage > Unity XT > Storage Admin > Dell Unity Dynamic Pools > Supported stripe widths
A dynamic pool’s stripe width, also known as the RAID width, is the number of drive extents used for the RAID type chosen for the pool. For example, a RAID 5 (4+1) RAID extent contains five drive extents. Four drive extents’ worth of space within the 4+1 RAID extent are used to store data, while one drive extent’s worth of space is used to store parity data. When creating a dynamic pool, the method in which the pool is created will determine if the stripe width is selected by the system, or by the user. When creating a pool through Unisphere CLI or REST API, the stripe width is specified by the user.
When creating a dynamic pool in Unisphere, the user selects the RAID type desired, but the stripe width is selected by the system automatically. The stripe width selected by the system directly depends on the number of drives selected at pool creation. Table 1 shows the various supported RAID types, and the correlation between the number of drives selected during pool creation and the stripe width Unisphere selects. For example, when RAID 5 is selected during pool creation in Unisphere, and eight drives are selected, the stripe width is automatically set to 4+1 by the system. If the drive count is 14 or more for RAID 5, a 12+1 width is selected. The selection of the larger stripe widths provides more usable capacity to the user. If you would like to force the system to choose a particular width, select only a specific number of drives at pool creation and later expand the pool with the remaining drives.
Table 1 Unisphere selected stripe widths based on drive count
RAID type | Number of drives at pool creation | Stripe width selected |
RAID 5 | 6 to 9 | 4+1 |
RAID 5 | 10 to 13 | 8+1 |
RAID 5 | 14 or more | 12+1 |
RAID 6 | 7 or 8 | 4+2 |
RAID 6 | 9 or 10 | 6+2 |
RAID 6 | 11 or 12 | 8+2 |
RAID 6 | 13 to 14 | 10+2 |
RAID 6 | 15 or 16 | 12+2 |
RAID 6 | 17 or more | 14+2 |
RAID 1/0 | 3 or 4 | 1+1 |
RAID 1/0 | 5 or 6 | 2+2 |
RAID 1/0 | 7 or 8 | 3+3 |
RAID 1/0 | 9 or more | 4+4 |