Dell PowerVault MD3820f - Manual (Page 16)

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 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
FC host connections may operate at 16 Gbps or at a lower data rate. Ports for 16 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.
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.
Figure 8. Fiber Optic Cable Connection
1. SFP transceiver 2. fiber optic cable
The RAID expansion ports support SAS expansion connections.
16