24 PowerEdge R720 and R720xd Technical Guide
Reliability, availability, and serviceability (RAS) features help keep the system online and operational 
without significant impact to performance, and can decrease data loss and crashing due to errors. 
RAS aids in rapid, accurate diagnosis of faults which require service. Table 10 describes the memory 
RAS features supported on the R720 and R720xd. 
 
Increased memory reliability can be a result from this selectable platform profile 
that adjusts parameters to reduce faults regarding refresh rates, speed, 
temperature and voltage 
Demand scrubbing is the ability to write corrected data back to the memory once 
a correctable error is detected on a read transaction. Patrol scrubbing proactively 
searches the system memory, repairing correctable errors. 
Recovery from Single DRAM Device Failure (SDDC) provides error checking and 
correction that protects against any single memory chip failure as well as multi-bit 
errors from any portion of a single memory chip.  
This feature provides the ability to identify a specific failing DIMM channel pair, 
thereby enabling the user to replace only the failed DIMM pair. 
Memory mirroring is a method of keeping a duplicate (secondary or mirrored) 
copy of the contents of memory as a redundant backup for use if the primary 
memory fails. The mirrored copy of the memory is stored in memory of the same 
processor socket. 
This feature provides the ability to detect transient errors on the address lines of 
the DDR channel. 
Memory sparing allocates one rank per channel  as a spare. If excessive 
correctable errors occur in a rank or channel, they are moved to the spare area 
while the operating system is running to prevent the errors from causing an 
uncorrectable failure. 
This feature helps to optimize power/performance and can also be used to 
prevent DIMMs from overheating.  
For information on memory mirroring and sparing configurations, see the 
Dell PowerEdge R720 and 
R720xd Owner’s Manual 
on Support.Dell.com/Manuals. Memory RAID is not supported.