IBM eserver i5 Handbook page 386

5486IOA.fm
units. It also supports internal tape devices, CD-ROM, and DVD units. The #2780
has four Ultra4 SCSI buses.
The #2780 is designed to work as a high performance controller for disks
protected by system mirroring or disks with no protection. In a RAID-5
configuration, disk unit protection is provided at less cost than mirroring, and with
greater performance than system checksums. DASD compression is not
supported. When used in an AIX or Linux environment, the #2780 can help
provide significant speed and throughput improvements.
The #2780 controls up to two removable media devices (internal tape, CD-ROM,
and DVD).
The #2780 is not supported in the system unit of the Model 520, 550, 570, or
595.
The number of disk units per #2780 varies by configuration:
Up to 20 disk units per #2780 are supported in a #5094 PCI-X Expansion
Tower attached to a Model 520, 550, 570, or 595.
Up to 18 disk units per #2780 are supported in the system unit or external
tower disk cage of the Model 270, 800, and 810.
Up to 15 disk units per #2780 are supported in a #9094 Base PCI I/O
Enclosure attached to a Model 870, 890,595
For all other configurations, contact your IBM marketing representative.
A minimum of three disk units of the same capacity is needed for a valid RAID-5
configuration. A maximum of six arrays is allowed per controller, with a maximum
of 18 disk units allowed per array.
Parity is spread across either two, four, eight, or 16 disk units in an array,
dependent upon the number of disk units started in the array, as represented in
the following table.
Number of units in the array
3
4 - 7
8 - 15
16 - 18
IBM Eserver i5 and iSeries System Handbook
352
Draft Document for Review October 18, 2004
Number of units parity is spread across
2
4
8
16