This feature is a PCI-X SCSI controller with a maximum compressed write cache of 757MB. #2757 provides RAID-5 protection for internal disks and also supports internal tape units, CD-ROM and DVD-RAM. The #2757 has four SCSI buses that support up to 18 disk units. Hardware data compression is not supported.
In addition to providing RAID-5 protection for disks, #2757 is also 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.
A minimum of three disk units of the same capacity are needed for a valid RAID-5 configuration. A maximum of six arrays are allowed per controller, with a maximum of 18 disk units allowed per array. All disk units in an array must be of the same capacity. Parity is spread across either two, four, eight, or sixteen 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 fifteen disk units is started, parity is spread across eight disk units. If an array of sixteen to eighteen disk units is started, parity is spread across sixteen 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.
#2757 controls up to two removable media devices (internal tape, CD-ROM, DVD).
This feature requires OS/400 V5R2, plus updates.