IBM 2782 PCI-X RAID Disk Unit Ctlr

• SCSI RAID Controller

IBM 2782 is a PCI-X SCSI controller with a 40MB cache that provides RAID-5 protection for internal disks and also supports internal tape units, CD-ROM and DVD devices. #2782 has two SCSI buses that support up to 12 disk units. Hardware data compression is not supported. In addition to providing RAID-5 protection for disks, #2782 also works as a high-performance controller for disks protected by system mirroring, or disks with no protection. In the RAID-5 configuration, disk unit protection is provided at less cost than mirroring. A minimum of three disk units of the same capacity are needed for a valid RAID-5 configuration. A maximum of four arrays are allowed per controller, with a maximum of 12 disk units allowed per array. All disk units in an array must be of the same capacity. Parity is spread across either two, four, or eight disk units in an array. If an array of three disk units is started, parity is spread across two disk units. If an array of four to seven disk units is started, parity is spread across four disk units. If an array of eight to twelve disk units is started, parity is spread across eight disk units. The number of arrays and size of each array can be influenced by specifying an optimization of either balance, performance, or capacity in Operations Navigator when starting arrays. An optimization of balance is the default when starting arrays from the green screens. If disk units are included into an existing array, parity may be spread across less than the preferred number of disk units. In this case the RAID function must be stopped and started to redistribute the parity. #2782 controls up to two removable media devices (internal tape, CD-ROM, or DVD)