C-2
Cisco UCS C420 Server Installation and Service Guide
OL-27640-01
Appendix C RAID Controller Considerations
Supercap Power Modules (RAID Backup Units)
Supercap Power Modules (RAID Backup Units)
T
his 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 3-53
).
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-2
lists 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.
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 3-43
):
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
.
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
