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Dell Storage Manager 2020 R1 Administrator's Guide

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Failure Scenarios

The FluidFS cluster can tolerate a single NAS controller failure without impact to data availability and without data loss. If one NAS controller in a NAS appliance becomes unavailable (for example, because the NAS controller failed, is turned off, or is disconnected from the network), the NAS appliance status is degraded. Although the FluidFS cluster is still operational and data is available to clients, you cannot perform most configuration modifications, and performance might decrease because data is no longer cached.

The impact to data availability and data integrity of a multiple NAS controller failure depends on the circumstances of the failure scenario. Detach a failed NAS controller as soon as possible, so that it can be safely taken offline for service. Data access remains intact as long as one of the NAS controllers in each NAS appliance in a FluidFS cluster is functional.

The following table summarizes the impact to data availability and data integrity of various failure scenarios.

Scenario System Status Data Integrity Comments
Single NAS controller failure Available, degraded Unaffected
  • Peer NAS controller enters journaling mode
  • Failed NAS controller can be replaced while keeping the file system online
Sequential dual‑NAS controller failure in single NAS appliance cluster Unavailable Unaffected Sequential failure assumes enough time is available between NAS controller failures to write all data from the cache to disk (Storage Center or nonvolatile internal storage)
Simultaneous dual-NAS controller failure in single NAS appliance cluster Unavailable Lose data in cache Data that has not been written to disk is lost
Sequential dual‑NAS controller failure in multiple NAS appliance cluster, same NAS appliance Unavailable Unaffected Sequential failure assumes enough time is available between NAS controller failures to write all data from the cache to disk (Storage Center or nonvolatile internal storage)
Simultaneous dual‑NAS controller failure in multiple NAS appliance cluster, same NAS appliance Unavailable Lose data in cache Data that has not been written to disk is lost
Dual‑NAS controller failure in multiple NAS appliance cluster, separate NAS appliances Available, degraded Unaffected
  • Peer NAS controller enters journaling mode
  • Failed NAS controller can be replaced while keeping the file system online

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