Dell PowerVault MD3420 - Manual (Page 15)

Storage Array Thermal Shutdown
The system automatically shuts down when system temperature exceeds the safe threshold. The battery
backup unit protects against data loss by providing power to offload cache to non-volatile memory in the
event of power loss. It is not necessary to shut down any MD1200 Series expansion enclosures attached
to the storage array when thermal shutdown occurs.
Temperature threshold values determine the temperature at which shutdown occurs. These thresholds
cannot be changed.
Table 1. Shutdown Threshold Type
Threshold Temperature Exceeding Event Description
Nominal failure threshold A critical event is set.
Maximum failure threshold Shutdown of the system power supplies occurs
within 3 minutes.
Shutdown threshold Shutdown of the system power supplies occurs
within 5 seconds.
System Password Reset
The storage array password can be reset if it is forgotten. To reset the password, push and hold down the
password reset switch for at least 5 seconds. The password is deleted.
The RAID controller module allows you to change the password.
NOTE: The reset switch can be accessed by using a small object such as the tip of a pen.
Cache Functions and Features
Cache Mirroring
Cache mirroring function copies accepted host-write data from the primary controller to the partner
controller. This action ensures that host-write data is safely mirrored to the partner controller before
successful completion status is returned to the host. If a controller fails, the surviving controller safely
retains all mirrored data. Cache mirroring is enabled by default.
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
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