IBM 2778 is an Ultra2 SCSI controller with a maximum compressed write cache size of 104MB that provides RAID-5 protection and compression (not on 70GB or larger disk units) for internal disks and also supports internal tape units, CD-ROM, DVD-RAM and DVD-ROM units.
The #2778 supports both disk compression and enhanced modes. The mode of operation is determined by a hardware jumper.
The #2778 is shipped in enhanced mode, which enables compression of the write cache. By moving the hardware jumper the controller will function in disk compression mode. In addition to providing RAID-5 protection for disks, the #2778 also works as a high-performance controller for disks protected by system mirroring, or disks with no protection. The #2778 controller supports up to 15 disk units. A minimum of four 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 ten disk units allowed per array. All disk units in an array must be of the same capacity. Parity is spread across four disk units for arrays of four to seven disk units. Parity can be spread across either four or eight disk units for arrays of eight or ten disks. For systems started with eight to ten disk units in an array the parity, for that array, will be spread across eight disk units. For systems that are started with less than eight disk units in the array and later increased to eight, nine or ten disk units, the RAID function must be stopped and then started before the parity will be spread across eight disk units.
The #2778 an also control up to two removable media devices (internal tape, CD, or DVD). The #2778 does not support compression on 70GB or larger disk units.