In Dell PowerFlex, Maintenance Mode is a critical operational state used primarily when a node requires software upgrades, firmware patches, or physical hardware replacement. When a Storage Data Server (SDS) requires maintenance, it cannot simply be powered down, as this would cause a rebuild of data to restore redundancy, placing immense stress on the cluster.
There are two types of maintenance modes:
Protected Maintenance Mode (PMM): This is the standard method for planned maintenance. The system identifies the data residing on the target node and makes a temporary copy (mesh-mirrors) of that data onto other nodes in the cluster before the node enters maintenance. This ensures that the cluster maintains full data protection (usually 2 copies) even while the node is offline.
Instant Maintenance Mode (IMM): This is used when time is critical, or the node is already offline. It acknowledges the node is down but does not trigger a full rebuild immediately, relying on the remaining copy of data.
Therefore, the specific purpose is to allow administrators to perform necessary software upgrades or hardware swaps in a controlled manner that manages data integrity and prevents unnecessary "storm" traffic from rebuilding data.
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