Technologies for the ProLiant ML570 G4 and ProLiant DL580 G4 servers

Errors in memory
As memory capacity grows, it becomes statistically more likely that memory errors will occur: both
hard and soft errors. Errors can be categorized as either correctable or uncorrectable. In the ProLiant
ML570 G4 and the DL580 G4 servers, the memory controller calculates check bits every time it writes
to memory. When memory is read, it re-calculates those check bits from the data stored in the DRAM
devices and compares the re-calculated check bits to the stored check bits. If the two sets of check bits
are different, the error can be corrected if it is a:
• Single-bit error in a DRAM device (correctable by standard ECC)
• Multi-bit error in a DRAM device (correctable by advanced ECC)
If multi-bit failures occur in different DRAM devices, they are not correctable. The uncorrectable error
will return bad data unless the customer has enabled Advanced Memory Protection techniques such
as Hot Plug RAID or Hot Plug Mirrored Memory.
For more information about the types and causes of memory errors, refer to the HP technology brief
titled “
HP Advanced Memory Protection technologies.”
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High-availability memory technologies
The ML570 G4 and DL580 G4 servers offer three levels of Advanced Memory Protection that provide
increased fault tolerance for applications requiring higher levels of availability: Online Spare, Hot
Plug Mirrored Memory, and Hot Plug RAID.
Supported Advanced Memory Protection technologies
Customers have four options to consider for memory protection in the ML570 G4 and the DL580 G4
servers: Advanced ECC , Online Spare, Hot Plug Mirroring, and Hot Plug RAID.
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
errors and does not provide any capability of replacing failed or degraded DIMMs without shutting
down the server.
Online Spare memory reduces the likelihood of uncorrectable memory errors but does not protect
against uncorrectable memory errors. Like advanced ECC, Online Spare provides no capability of
replacing failed or degraded DIMMs without shutting down the server. The amount of memory
reserved for the Online Spare rank will vary from one system configuration to the next. The exact
percentage of memory available to the OS when using Online Spare mode depends on the number
and size of DIMMs populated per memory board.
Hot Plug Mirrored Memory provides protection against both correctable and uncorrectable memory
errors. Hot Plug Mirrored Memory also allows replacing failed or degraded DIMMs while the system
is operating. However, this mode uses half of the installed memory for redundancy.
Hot Plug RAID memory often provides the most economical and effective memory protection. Like Hot
Plug Mirrored Memory, it protects against correctable and uncorrectable memory errors, but it does
so while allowing 75 percent of the installed memory to be available to the OS. Hot Plug RAID
memory also allows replacing failed or degraded DIMMs while the system is operating.
Table 1 summarizes differences in functionality among the levels of memory protection.
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Available at this URL: www.hp.com/servers/technology
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