Home > Storage > PowerScale (Isilon) > Product Documentation > Management and Migration > Storage Tiering with Dell PowerScale SmartPools > Disk pools
Disk pools are the smallest unit within the storage pools hierarchy, as illustrated in Figure 5. OneFS provisioning works on the premise of dividing similar nodes’ drives into sets, or disk pools, with each pool representing a separate failure domain.
These disk pools are protected by default at +2d:1n (or the ability to withstand the failure of two disks or one entire node). The disk pools span from four to twenty nodes with modular, chassis-based platforms. Each chassis contains four compute modules (one per node), and five drive containers, or “sleds,” per node.
Each sled is a tray that slides into the front of the chassis and contains between three and six drives, depending on the configuration of a particular node chassis. Disk pools are laid out across all five sleds in each node. For example, a chassis-based node with three drives per sled would have the following disk pool configuration:
Note: Earlier generations of Isilon hardware and the current PowerScale nodes use six-drive node pools that span from three to forty nodes.
Each drive may belong to only one disk pool. Data protection stripes or mirrors do not extend across disk pools (the exception being a Global Namespace Acceleration extra mirror, as described in Global Namespace Acceleration). OneFS manages disk pools. Users cannot configure disk pools.