Disk subsystems
IBM® TotalStorage® Disk subsystems (Enterprise Storage System - ESS, or DS) are large disk subsystems that are typically configured to provide RAID-5 and RAID-10 volumes. They contain two System p® servers connected to the system backplane to manage and monitor the system.
The disk drives are configured to provide groups of logical disks that are divided into partitions. A data partition in a disk group is referred to as a volume. Each volume is associated with a logical unit number (LUN) that is a subdivision of the physical disk on a storage system.
The disk subsystems have connections to:
- System p (or other) host servers over SCSI or Fibre Channel links
- Other disk subsystems over ESCON® or Fibre Channel links. (PPRC uses these physical links to mirror data.)
- ESSNet, the local management Ethernet network for the ESS
Commands sent over this network configure and manage PPRC through ESS Copy Services.
- Nodes that access stored data.
Note: PowerHA® SystemMirror® Enterprise Edition for
Metro Mirror requires that inter-storage links be available to carry
data in both directions at the same time. If ESCON links are used, a minimum of two ESCON links is required because
each link can carry data in only one direction at a time. You should
have at least four links to improve throughput and to provide redundancy
of the ESCON cables and adapters.