Storage Array Thermal Shutdown; System Password Reset; Cache Functions And Features; Cache Mirroring - Dell EMC PowerVault MD3820i Owner's Manual

NOTE: For virtual disks, the RAID controller firmware changes the data cache setting based on the state of the battery. If
the battery is missing or does not have sufficient charge, the controller flushes the cache and sets the write cache attribute
to Write Through for all virtual disks. When the battery is replaced, Write Back is re-enabled.

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 5. Shutdown Threshold Type
Threshold Temperature Exceeding
Nominal failure threshold
Maximum failure threshold
Shutdown threshold

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.
NOTE: The password reset switch is not available if your system was shipped after September, 2015. The password reset
switch functionality was disabled starting from controller firmware 08.20.09.60 and later versions.

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 power failure is less likely to cause loss of data.
Event Description
A critical event is set.
Shutdown of the system power supplies occurs
within 3 minutes.
Shutdown of the system power supplies occurs
within 5 seconds.
Controller Modules 13