IBM 250000 - Manual (Page 6)

Leadership enterprise server with significantly lower cost of ownership in a highly available and
expandable, rack-dense, 1U dual-socket server
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This new processor design comes with some trade-offs in memory capacity, performance, and
cost: For example, greater memory capacity comes with lower memory speed. Alternatively, it
is possible to achieve the same memory capacity at lower cost but at a lower memory speed.
Regardless of memory speed, the Xeon 5500 platform represents a significant improvement in
memory bandwidth over the previous Xeon 5400 platform. At 1333MHz, the improvement is
almost 500% over the previous generation. This huge improvement is mainly due to the dual
integrated memory controllers and faster DDR-3 1333MHz memory. Throughput at 800MHz is 25
gigabytes per second (GBps); at 1066MHz it’s 32GBps; and at 1333MHz it’s 35GBps. This
improvement translates into improved application performance and scalability.
Memory interleaving refers to how physical memory is interleaved across the physical DIMMs. A
balanced system provides the best interleaving. A Xeon 5500 processor-based system is
balanced when all 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 x3550 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).
Drive Bays
The x3550 M2 contains six drive bays in all. Hot-swap drives may be inserted or removed
through the front of the server without powering off the system. Simple-swap solid-state drives
can be inserted or removed through the front of the server as well; however, the system power
must first be turned off.
For additional storage, a direct-attach, NAS or SAN external expansion option can be added,
using an optional controller.
A 24X/24X/24X/8X 5 speed (ultraslim, 0.5”) CD-RW/DVD-ROM Combo drive with an IDE interface
ships standard in all x3550 M2 servers. No diskette drive is supplied with any model; an external
USB floppy drive may be used, if needed.
Disk Controllers
All SAS-equipped x3550 M2 models include an integrated hardware based ServeRAID-BR10i
SAS/SATA controller. This controller supports up to six internal SAS, SATA or solid-state
drives.
5 Variable read rate. Actual playback speed varies and is often less than the maximum possible.