Product Description
IBM 4778 PCI RAID Disk Unit Controller
- SCSI RAID Controller
IBM 4778/9778 is a 3-Port Ultra2 SCSI Ccontroller that provides support for internal SCSI Disk Units, Internal Tape Units, CD-ROM and DVD-RAM units. The Controller has a maximum compressed write cache size of 104MB that provides RAID-5 protection. Compression is supported for internal Disk Units up to 35GB Disk Unit capacity. #4778/#9778 support both disk compression and enhanced modes. The mode of operation is determined by a hardware jumper. It is shipped in enhanced mode, which enables compression of the write cache and Extended Adaptive Cache. Feature #4331: 1.6GB Read Cache Device is needed for the OS/400 Extended Adaptive Cache function.) By moving the hardware jumper, the controller will function in disk compression mode. In addition to providing RAID-5 protection for disks, #4778/#9778 is also designed to work 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, and with greater performance than system checksums. The #4778/#9778 controllers support a maximum of 15 or 18 disk units depending on supported model. 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 to ten disk units. 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 an array and later field upgraded 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 #4778/#9778 controls up to two removable media devices (internal tape, CD-ROM or DVD-RAM).
