HP ProLiant xw460c Blade Workstation - Manual (Page 30)

Hardware options installation 30
In online spare mode, a single rank of memory acts as the spare memory. For single-rank FBDIMMs, the
entire FBDIMM acts as the spare memory. For a dual-rank FBDIMM, only half of the FBDIMM acts as the
spare memory while the other half is available for operating system and application usage.
If one of the non-spare FBDIMMs receives correctable memory errors at a higher rate than a specific
threshold, the server blade automatically copies the memory contents of the degraded rank to the online
spare rank. The server blade then deactivates the failing rank and automatically switches over to the
online spare. Because FBDIMMs that experience a high rate of correctable memory errors also have a
higher probability of receiving an uncorrectable memory error, this configuration reduces the likelihood of
uncorrectable memory errors that would result in server blade downtime.
Online spare is performed per branch of the memory controller. For a server blade with both branches
populated, two ranks are used for online spare memory. One branch can fail over to the associated
online spare while the other branch is still protected.
Each branch is made up of two banks:
• Branch 0 contains banks A and C
• Branch 1 contains banks B and D
Online spare FBDIMM configuration requirements (in addition to general configuration requirements):
• When only bank A is being used, it must be fully populated with dual-rank FBDIMMs.
• If banks A and C are being used, they must be fully populated.
• If installed, bank A and bank C must contain FBDIMMs with identical part numbers.
• If installed, bank B and bank D must also contain FBDIMMs with identical part numbers.
In online spare mode, FBDIMMs must be populated as specified in the following table:
Configuration Branch 0
Bank A
1A and 3A
Branch 0
Bank C
2C and 4C Branch 1
Bank B
5B and 7B Branch 1
Bank D
6D and 8D
1* X — — —
2 X X — —
3 X X X X
* Configuration 1 is only supported if using bank A, populated with dual-rank FBDIMMs.
After installing FBDIMMs, use RBSU to configure the system for online spare memory support
(" Configuring online spare memory " on page 47 ).
Mirrored memory configuration
Mirroring provides protection against uncorrectable memory errors that would otherwise result in server
blade downtime.
Mirroring is performed on the branch level. Branch 0 and branch 1 mirror each other.
Each branch maintains a copy of all memory contents. Memory writes go to both branches. Memory
reads come from only one of the two branches (unless an uncorrectable error occurs). If a memory read
on one branch returns incorrect data due to an uncorrectable memory error, the system automatically
retrieves the proper data from the other branch. A branch is not necessarily disabled (thus losing
mirroring protection) because of a single uncorrectable error. Mirroring protection is not lost because of
transient and soft uncorrectable errors, resulting in systems that maintain mirroring protection (and thus
improved uptime) unless there is a failure of both branches.
Mirrored memory FBDIMM configuration requirements (in addition to general configuration requirements):
• Banks A and B must be fully populated.