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MD System
The PowerVault MD array provides the storage capacity for NAS; the NX36x0 cannot be used as a stand‐
alone NAS appliance. The MD array eliminates the need for separate storage capacity for block and file
storage.
SAN Network
The NX36x0 shares a back‐end infrastructure with the MD array. The SAN network connects the NX36x0
to the MD system and carries the block level traffic. The NX36x0 communicates with the MD system
using the iSCSI protocol.
Internal Network
The internal network is used for communication between NAS controllers. Each of the NAS controllers in
the FluidFS system must have access to all other NAS controllers in the FluidFS system to achieve the
following goals:
• Provide connectivity for FluidFS system creation
• Act as a heartbeat mechanism to maintain high availability
• Enable internal data transfer between NAS controller
• Enable cache mirroring between NAS controllers
• Enable balanced client distribution between NAS controllers
Data Caching And Redundancy
New or modified file blocks are first written to a local cache, and then 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 (and asynchronously)
transferred to permanent storage using optimized data‐placement schemes.
When cache mirroring is not possible, such as during a single NAS controller failure or when the BPS
battery status is low, NAS controllers write directly to storage (journaling mode).
File Metadata Protection
File metadata includes information such as name, owner, permissions, date created, date modified, and a
soft link to the file’s storage location.
The FluidFS system has several built‐in measures to store and protect file metadata:
• Metadata is managed through a separate caching scheme and replicated on two separate volumes.
• Metadata is check-summed to protect file and directory structure.
• All metadata updates are journaled to storage to avoid potential corruption or data loss in the event of
a power failure.
• There is a background process that continuously checks and fixes incorrect checksums.
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