When a mirrored volume is created, Data ONTAP separates spare disks from a collection of disks, called a disk pool, into two disk pools, pool0 and pool1.
Disks from pool0 are used to create plex0 while disks from pool1 are used to create plex1.
Plexes local to the host node in an active/active configuration must be connected to the disk pool named pool0. Pool0 consists of the storage attached to host adapters in slots 3 through 7. Pool rules for MetroCluster configurations that use switches are different.
For more information about storage system slot assignments, see the System Configuration Guide.