Administrator Guide

(client VIPs) on the client network that allow clients to access the FluidFS cluster as a single entity. The client VIP also enables
load balancing between NAS controllers, and ensures failover in the event of a NAS controller failure.
If client access to the FluidFS cluster is not through a router (in other words, a flat network), define one client VIP per NAS
controller. If clients access the FluidFS cluster through a router, define a client VIP for each client interface port per NAS
controller.
Data Caching and Redundancy
New and modified files are first written to the cache, and then cache data is immediately mirrored to the peer NAS controller
(mirroring mode). Data caching provides high performance, while cache mirroring between peer NAS controllers ensures data
redundancy. Cache data is ultimately transferred to permanent storage asynchronously through optimized data-placement
schemes.
When cache mirroring is not possible, such as a single NAS controller failure or when the BPS battery status is low, NAS
controllers write directly to storage (journaling mode).
File Metadata Protection
The FluidFS cluster has several built-in measures to store and protect file metadata (which includes information such as name,
owner, permissions, date created, date modified, and a soft link to the file’s storage location).
● All metadata updates are recorded constantly to storage to avoid potential corruption or data loss in the event of a power
failure.
● Metadata is replicated on two separate volumes.
● Metadata is managed through a separate caching scheme.
● Checksums protect the metadata and directory structure. A background process continuously checks and fixes 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 traffic 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 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)
FluidFS Administration 341