IBM X3400 M2 Product Manual page 5

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memory channels on a socket have the same amount of memory.
A memory rank is simply a segment of memory that is addressed by a specific address bit. DIMMs
typically have 1, 2 or 4 memory ranks, as indicated by their size designation.
• A typical memory DIMM description is 2GB 4Rx8 DIMM
• The 4R designator is the rank count for this particular DIMM (R for rank = 4)
• The x8 designator is the data width of the rank
It is important to ensure that DIMMs with appropriate number of ranks are populated in each channel for
optimal performance. Whenever possible, it is recommended to use dual-rank DIMMs in the system.
Dual-rank DIMMs offer better interleaving and hence better performance than single-rank DIMMs. For
instance, a system populated with six 2GB dual-rank DIMMs outperforms a system populated with six 2GB
single-rank DIMMs by 7% for SPECjbb2005. Dual-rank DIMMs are also better than quad-rank DIMMs
because quad-rank DIMMs will cause the memory speed to be down-clocked.
Another important guideline is to populate equivalent ranks per channel. For instance, mixing one single-
rank DIMM and one dual-rank DIMM in a channel should be avoided.
Note: It is important to ensure that all three memory channels in each processor are populated. The
relative memory bandwidth decreases as the number of channels populated decreases. This is because
the bandwidth of all the memory channels is utilized to support the capability of the processor. So, as the
channels are decreased, the burden to support the requisite bandwidth is increased on the remaining
channels, causing them to become a bottleneck.
For increased availability, the x3400 M2 offers an additional (but mutually exclusive) level of IBM Active
Memory protection: online memory mirroring.
Memory mirroring works much like disk mirroring. The total memory is divided into two channels. Data is
written concurrently to both channels. If a DIMM fails in one of the DIMMs in the primary channel, it is
instantly disabled and the mirrored (backup) memory in the other channel becomes active (primary) until
the failing DIMM is replaced. One-half of total memory is available for use with mirroring enabled. (Note:
Due to the double writes to memory, performance is affected.)
Mirroring is handled at the hardware level; no operating system support is required.
DDR-3 memory is available in 1GB, 2GB, 4GB and 8GB DIMMs. DIMMs are installed individually (not in
pairs).
Hot-Swap/Redundant Components
System availability is maximized through the extensive use of hot-swap and redundant components,
including:
• Redundant memory protection (with memory mirroring enabled) and Chipkill protection
• Hot-swap, redundant hard disk drives (with RAID-1/10 protection standard, and RAID-1E/5/6
protection optional)
Large HDD Storage Capacity
The x3400 M2 offers a choice of disk storage, supporting up to four 3.5-inch hot-swap or simple-swap
Serial ATA (SATA) drives, four 3.5-inch hot-swap high-performance Serial-Attach SCSI (SAS) drives or
eight 2.5-inch hot-swap SAS drives:
3.5-inch SAS
• 15,000 RPMs — 73.4, 146.8, or 300GB (2.4TB maximum)
2.5-inch SAS
• 10,000 RPMs — 146.8 or 300GB (2.4TB)
• 15,000 RPMs — 73.4 or 146.8GB (1.17TB)
3.5-inch SATA—Hot-Swap
• 10K RPMs — 160, 250, 500, 750GB or 1TB (4.0TB)
3.5-inch SATA—Simple-Swap
• 10K RPMs — 160, 250, 500 or 750GB (3.0TB)
Notes: Hot-swap and simple-swap SATA drives offer exactly the same reliability as fixed SATA drives.
Only the system availability improves using the swappable drives. (Less downtime is incurred removing
and installing the drives.) Hot-swap SAS drives use the Converged Tray for interchangeability with other
™
IBM System x systems.
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