Drive Bays - IBM 79784AU Product Manual

A highly available and expandable, rack-dense, 1U dual-socket SMP server, for application
serving in Web environments
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Variable read rate. Actual playback speed varies and is often less than the maximum possible.
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DDR II ECC Fully Buffered Memory with Chipkill Protection
The x3550 supports up to 32GB of memory in 8 DIMM sockets. Some models include two
512MB DIMMs standard, while others ship with two 1GB DIMMs. The x3550 uses PC2-5300
fully-buffered double data rate II (DDR II) memory (operating at 667MHz) for faster access, and
provides Active Memory features, including advanced Chipkill memory protection, for up to 16X
better error correction than standard ECC memory.
The fully buffered memory in the x3550 provides up to triple the memory bandwidth (up to
21.3GBps in four channels of PC2-5300 fully-buffered DIMMs vs. a maximum of 6.4GBps in two
channels of unbuffered PC2-3200 memory and up to double the system memory capacity (8
DIMMs x 4GB) of the predecessor x336 server (8 DIMMs x 2GB). By performing reads and writes
simultaneously, it eliminates the previous memory read-to-write blocking latency. In addition, it
also offers innovative data reliability and security features to help improve data integrity, including
enhanced CRC protection, data retry on error detect and buffer registers for improved fault
isolation.
For increased availability, the x3550 offers two additional (but mutually exclusive) levels of IBM
Active Memory protection: online memory mirroring, and online hot-spare memory.
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. Mirroring can be accomplished with multiples
of four DIMMs (one pair per memory channel). Up to 16GB (four 4GB DIMMS) of memory is
available for use with mirroring enabled. (Note: Due to the double writes to memory, performance
is affected.)
When online hot-spare memory is enabled, using single and/or dual-rank DIMMs one rank is set
aside per branch as online spares in case one of the other ranks fails. The spare rank must have
capacity at least that of the largest active rank. Up to 24GB (using 8 single-rank 4GB DIMMs) or
28GB (using 8 dual-rank 4GB DIMMs) of memory is available when the hot-spare feature is
active. (The lowest-numbered rank of those with the highest capacity in each branch is used for
the hot-spares.)
Either of these features requires operating system support.
When multiples of four DIMMs (4 or 8) are installed, the x3550 operates in four-way interleaved
mode, for higher performance. When only two DIMMs are used, the system defaults to two-way
interleaved mode.
DIMMs must be installed in pairs. Memory is available in kits consisting of two 512MB, 1GB, 2GB
or 4GB DIMMs.

Drive Bays

The x3550 contains either two or four drive bays in all, depending on the model. Some models
offer two 3.5-inch bays that support hot-swap SAS or simple-swap SATA II drives. This
enables up to two slimline (1.0") drives to be installed, totaling up to 600GB (SAS) or 2TB
(SATA).
Other models feature four 2.5-inch bays that support hot-swap SAS drives totaling up to
587.2GB.
Hot-swap drives may be inserted or removed through the front of the server without powering off
the system. Simple-swap 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.
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A 24X/24X/24X/8X speed (ultraslim, 0.5") CD-RW/DVD-ROM Combo drive with an IDE interface
ships standard in all x3550 servers. No diskette drive is supplied with any model; an external
USB floppy drive may be used, if needed.
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