Technologies for the ProLiant ML570 G3 and ProLiant DL580 G3 Servers Technology Brief

The ProLiant ML570 G3 and the DL580 G3 support mirroring of two or four memory boards,
allowing the server to be completely protected from memory failures. However, the customer
effectively uses half of the installed memory capacity (for example, if 4 GB is installed, only 2GB is
available to the OS and applications).
The mirroring functionality requires no OS support but does require each installed memory board to
have the same total amount of memory. The mirroring function supports hot-replace without any OS
support. For this reason, mirrored memory mode is beneficial to businesses that cannot afford
downtime and cannot risk waiting until scheduled downtime to replace degraded memory modules.
Hot Plug RAID
HP introduced Hot Plug RAID memory in its 8-way ProLiant servers using the F8 architecture. Hot Plug
RAID memory protects the server against uncorrectable memory errors that would otherwise result in a
server failure. If Hot Plug RAID memory is enabled, then the north bridge uses an exclusive-OR engine
to generate a parity check line for every three cache lines. The north bridge interleaves the cache
lines and the parity check line across all four memory boards (Figure 8). If an uncorrectable memory
error is encountered, the server can re-create the proper data using the parity information and the
information from the other memory boards that contain no failures.
Therefore, to use Hot Plug RAID memory, administrators must install all four memory boards in the
ProLiant ML570 G3 and the DL580 G3 servers. Because the cache lines are striped across the
memory boards, all four boards must have the same total amount of memory.
As with Hot Plug Mirrored Memory, Hot Plug RAID memory allows failed or degraded DIMMs to be
replaced while the server is running without requiring server downtime. The memory board with the
failed DIMMs can be removed, failed DIMMs replaced, and the board re-inserted into the server
without any interruption to the OS. Furthermore, using Hot Plug RAID provides the most cost-effect
means of protecting against uncorrectable errors, because only 25 percent of the memory is allocated
to parity information.
Figure 8. Hot Plug RAID memory for the ProLiant ML570 G3 and DL580 G3 stripes three cache lines and the associated parity
information across the memory boards.
Comparing Advanced Memory Protection technologies
Customers have several options to consider when evaluating the different memory protection options
in the ProLiant ML570 G3 and the DL580 G3 servers.
Generally, as the level of memory availability (redundancy) increases, the amount of installed memory
available for use by the OS decreases. Advanced ECC provides the most available memory, as all
installed memory is available to the OS and applications. Advanced ECC mode protects against
correctable memory errors. However, advanced ECC mode does not protect against uncorrectable
14