Dell PowerFlex 4.6.x Technical Overview

Instant maintenance mode

Using instant maintenance mode, you can restart a server hosting an SDS without requiring a shutdown or interrupting application I/Os. Storing all writes created during maintenance to a dedicated fault set prevents data loss if there is a single failure.

Instant maintenance mode enables you to restart a server that hosts an SDS, with minimal impact on PowerFlex, thus bypassing the disruption and effort caused by disorderly shutdown, protection domain shutdown, and orderly shutdown.

Whereas PowerFlex always uses two copies of user data, invoking maintenance mode introduces an additional copy that stores all writes created during maintenance to an SDS or fault set (created during maintenance) in both a primary location and a new location. This copy prevents data loss if a single failure occurs.

When the SDS or fault set is returned from maintenance mode, only the new writes are required to be resynchronized, thus minimizing data transfer during and after the update.

Instant maintenance mode does not interrupt application I/Os; it can be run on any amount of members of a fault set; and it can run in parallel on different protection domains. While an SDS is in maintenance mode, most PowerFlex operations (like adding a volume) cannot be performed in the fault set, protection domain, or storage pool in which the SDS and its devices reside.

To invoke maintenance mode, the following conditions are required:

• Only one fault unit (or stand-alone SDS) can be in maintenance mode at any given time.
• No other SDSs can be in a degraded or failed state (force override can be used).
• There must be adequate space on other SDSs for the additional backup (force override can be used).
  NOTE: Use of force override options when entering maintenance mode can lead to data unavailability while maintenance mode is activated.

  While an SDS is in maintenance mode, it can be shut down with no danger to data.