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System Design Deep Dive: Real-World Distributed Systems

Metadata Consistency Model of GFS

Learn how GFS can provide strong consistency for the metadata mutations.

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Metadata

The manager node stores all of the metadata in memory and serves user requests from there for good performance. Some part of the metadata is stored persistently on the hard disk of the manager node and also replicated on remote machines, while some metadata is not, as shown in the following illustration. (The part of the metadata that is not persistently stored can be rebuilt if needed. At times, such data is called a soft state.)

Metadata stored in the manager's memory vs. metadata stored persistently on the hard disk
Metadata stored in the manager's memory vs. metadata stored persistently on the hard disk

Note: In February 2017, AWS's S3 storage system suffered an outagehttps://aws.amazon.com/message/41926/. As part of the recovery, some subsystems needed a full restart, which took ...