Dell MD3600f SFP Transceivers, Fiber Optic, and SAS Cables, Write-Back Cache, Write-Through Cache

Write–Back Cache

In write-back cache, write operations result in a completion signal being sent to the host operating system as soon as the cache receives the data to be written. The target physical disk receives the data at a more appropriate time in order to increase controller performance. In dual-active controller configurations with write-back caching enabled, the write data is always mirrored to the cache of the second controller before completion status is issued to the host initiator. Write-back cache is enabled by default unless cache mirroring is disabled.

Write–Through Cache

In write-through cache, data is written to the physical disk before completion status is returned to the host operating system. Write-through cache is considered more robust than write-back cache, since a power failure is less likely to cause loss of data. The RAID controller automatically switches to write-through if cache mirroring is disabled or if the battery is missing or has a fault condition.

SFP Transceivers, Fiber Optic, and SAS Cables

Figure 3-2 shows fiber optic cable and SFP transceivers.

NOTE: Your SFP transceivers and cables may look different from the ones shown below. The differences do not affect the performance of the SFP transceivers.

FC host connections may operate at 8 Gbps or at a lower data rate. Ports for 8 Gbps FC host connections require SFP transceivers designed for this data rate. SFP transceivers that support other data rates are incompatible.

WARNING: Do not disassemble or remove any part of a small form-factor pluggable (SFP) transceiver due to the possibility of being exposed to laser radiation.

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Planning: RAID Controller Modules