Cisco Systems UCS C420 manual Supercap Power Modules RAID Backup Units, RAID Controller Cabling

Appendix C RAID Controller Considerations

Supercap Power Modules (RAID Backup Units)

Supercap Power Modules (RAID Backup Units)

This server supports installation of two supercap power module (SCPM) backup units. The units mount to trays on the removable air baffle (see Replacing the Supercap Power Module (RAID Backup Unit), page 3-49).

The SCPM is available only when using the LSI MegaRAID-CV controller cards. This module provides approximately 3 years of backup for the disk write-back cache DRAM in the case of sudden power loss by offloading the cache to the NAND flash.

Mixing Drive Types in RAID Groups

Table C-2lists the technical capabilities for mixing hard disk drive (HDD) and solid state drive (SSD) types in a RAID group. However, see the best practices recommendations that follow for the best performance.

Table C-2 Drive Type Mixing in RAID Groups

Mix of Drive Types
in RAID Group	Allowed?
SAS HDD + SATA HDD	Yes
SAS SSD + SATA SSD	Yes
HDD + SSD	No

Best Practices For Mixing Drive Types in RAID Groups

For the best performance, follow these guidelines:

•Use either all SAS or all SATA drives in a RAID group.

•Use the same capacity for each drive in the RAID group.

•Never mix HDDs and SSDs in the same RAID group.

RAID Controller Cabling

The maximum two supported RAID controller cards should be populated in PCIe slots in the following order (see Figure 3-23 on page 3-40):

1.PCIe slot 3

2.PCIe slot 5

Refer to the following examples for cable routing guidelines:

•Example 1—One Nonexpander and One RAID Controller with Eight Drives, page C-3

•Example 2—Two Nonexpanders and Two RAID Controllers with 16 Drives, page C-4

•Example 3—Two Expanders and One RAID Controller with Sixteen Drives, page C-5

For more information about transition cards, see Replacing a Modular Drive Bay Assembly, page 3-14.

Cisco UCS C420 Server Installation and Service Guide

C-2 OL-27640-01