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Attention:
1. It is possible to lose data if a power outage occurs while using the write back
setting. Consider carefully whether to enable write back on a physical drive.
Depending on how you use the system, write back might be undesirable.
2. If you set this feature to write back, wait at least 10 seconds after your last
operation before you turn off your system. Failure to follow this practice might
result in lost data.
Write through
For the write-through setting, the controller sends data to the physical drive for
storage. Subsequently, the physical drive stores the data; then, sends a confirmation
to the controller. Using write through can decrease performance, but has no risk of
losing data.
More information
v Changing the write-cache mode on a physical drive (action)
v Fine-tuning your system
Understanding write-cache mode for logical drives
When using the write-cache-mode option, you can choose from two available
settings.
Write back
For the write-back setting, the operating system sends data to the controller to
write to a storage device. Subsequently, the controller sends a confirmation to the
operating system before actually writing the data to the storage device. Doing so
increases performance, but also contains an element of risk. For example, if there is
a power failure, the data currently in the controller cache is lost. This is no risk
when using a controller with a battery-backup cache. The battery preserves the
data in the controller cache in the event of a power failure.
Attention:
1. It is possible to lose data if a power outage occurs while using the write back
setting without a battery-backup cache device. If your controller does not have
a battery-backup cache installed and enabled, consider carefully whether to
enable write back on a logical drive. Depending on how you use the system,
write back might be undesirable.
2. If you do not have a battery-backup cache installed and enabled and you set
this feature to write back, wait at least 10 seconds after your last operation
before you turn off your system. Failure to follow this practice might result in
lost data.
Write through
For the write-through setting, the operating system sends data to the controller to
write to a storage device. Subsequently, the controller writes the data to the storage
device; then, sends a confirmation to the operating system. This setting can
decrease performance, but contains no risk of losing data.
More information
v Changing the write-cache mode on a logical drive (action)
v Fine-tuning your system
Chapter 4. Managing ServeRAID devices 193