Administrator Guide

• Checksums protect the metadata and directory structure. A background process continuously checks and xes incorrect checksums.
Load Balancing and High Availability
For availability and performance, client connections are load balanced across the available NAS controllers. Both NAS controllers in a NAS
appliance operate simultaneously. If one NAS controller in a NAS appliance fails, clients fail over automatically to the peer controller. When
failover occurs, some SMB clients will automatically reconnect to the peer NAS controller. In other cases, an SMB application might fail and
you must restart it. NFS clients experience a temporary pause during failover, but client network trac resumes automatically.
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 o, 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 conguration modications, 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 oine 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 Unaected
• Peer NAS controller enters journaling mode
• Failed NAS controller can be replaced while
keeping the le system online
Sequential dual‑NAS controller
failure in single NAS appliance
cluster
Unavailable Unaected 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 Unaected 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 Unaected
• Peer NAS controller enters journaling mode
• Failed NAS controller can be replaced while
keeping the le system online
FluidFS Administration 357