Installation guide

IBM Eserver xSeries 366 Technical Introduction 17
SAS 1.0 technology is replacing Ultra320 SCSI in SCSI and RAID controllers. Beyond the
upgrades in I/O processor and memory speeds, SAS-based products will differ from
SCSI-based products in the following ways:
򐂰 Higher bandwidth
Ultra320 SCSI supports 320 MBps of bandwidth per channel. SAS 1.0 supports 3 Gbps
(approximately 300 MBps) of bandwidth per port. So although the two Ultra320 SCSI
channels of the ServeRAID-6M can potentially support 640 MBps of bandwidth, the
onboard SAS controller with its 8 ports could support up to 24 Gbps (approximately
2.4 GBps) of bandwidth. Therefore, bandwidth is limited by PCI-X or PCI Express bus
speeds.
򐂰 Greater drive support
SCSI-based products support 14 drives per channel. By cascading drive enclosures,
SAS-based products will support up to 72 drives per 4 ports. Although this is not directly
relevant to the x366 and the ServeRAID-8i because the supported SAS drives are only in
the six internal drive bays, it is indicative of the advances in the technology and the future
capabilities of ServeRAID SAS adapters with external storage connectivity.
The SCSI subsystem includes an Adaptec AIC-9410 single chip Serial Attached SCSI (SAS),
which does not support any RAID. To enable RAID support, an optional ServeRAID-8i SAS
RAID controller (part number 13N2227) can be installed in a dedicated slot. The
ServeRAID-8i enables the following RAID levels:
򐂰 RAID-0
򐂰 RAID-1
򐂰 RAID-1E
򐂰 RAID-5
򐂰 RAID-5EE
򐂰 RAID-6
򐂰 RAID-10
򐂰 RAID-60 (although the x366 does not support this RAID level since it requires 8 drives)
The ServeRAID-8i has the following possible stripe sizes: 16 KB, 32 KB, 64 KB, 128 KB,
256 KB, and 512 KB. 64 KB is the default stripe size. The adapter supports up to 24 logical
drives. The ServeRAID-8i does not have any connectors for external SAS devices.
The ServeRAID-8i supports two additional RAID levels compared to other ServeRAID
controllers:
򐂰 RAID-6 is a multiparity type that requires a minimum of four drives, of which two drives’
worth of capacity are consumed for redundancy. RAID-6 allows the loss of two drives
without data loss, but this loss is associated with a substantial performance degradation.
򐂰 RAID-60 is a hierarchical array made up of multiple RAID-6 arrays at the lower level with
data striped over these arrays (the 0 in 60) at the upper level. Even though the
ServeRAID-8i supports this RAID level, it is not supported on the x366 because it requires
a minimum of 8 drives.
For external SCSI disk enclosures attachment, such as the EXP400, the ServeRAID-6M can
be installed. Because this card is based on SCSI architecture, it is incompatible with the SAS
subsystem and therefore cannot be used to run the internal disks.
The following drives are supported in the x366:
򐂰 36.4 GB, 10 K RPM 2.5” SAS drive, part number 26K5654
򐂰 73.4 GB, 10 K RPM 2.5” SAS drive, part number 26K5655