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Questions and Answers
What type of interfaces do distributed storage facilities need to export?
What type of interfaces do distributed storage facilities need to export?
Which aspect helps managers determine the inventories and delivery times accurately in distributed storage facilities?
Which aspect helps managers determine the inventories and delivery times accurately in distributed storage facilities?
What is a characteristic of some distributed storage facilities that provide both storage and processing services?
What is a characteristic of some distributed storage facilities that provide both storage and processing services?
How do distributed file systems ensure consistency when files are updated by clients?
How do distributed file systems ensure consistency when files are updated by clients?
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In which situation is a replica of a file maintained on other server machines in a distributed file system?
In which situation is a replica of a file maintained on other server machines in a distributed file system?
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What type of interface allows operating systems to utilize multiple types of storage devices regardless of location?
What type of interface allows operating systems to utilize multiple types of storage devices regardless of location?
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How are files typically stored in a distributed file system where the file server is distributed across multiple machines?
How are files typically stored in a distributed file system where the file server is distributed across multiple machines?
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'Cache coherence algorithms' mentioned in the text are necessary for what purpose in distributed file systems?
'Cache coherence algorithms' mentioned in the text are necessary for what purpose in distributed file systems?
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'DFS' in the context provided stands for:
'DFS' in the context provided stands for:
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'VFS' mentioned in the text is an abbreviation for:
'VFS' mentioned in the text is an abbreviation for:
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What is one of the benefits of load balancing client requests across all replicas?
What is one of the benefits of load balancing client requests across all replicas?
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Why is write-update to the file system state more complex when dealing with replicas?
Why is write-update to the file system state more complex when dealing with replicas?
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What is one downside of forcing every write-update to every replica?
What is one downside of forcing every write-update to every replica?
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How does partitioning contribute to greater availability in the file system compared to a single server design?
How does partitioning contribute to greater availability in the file system compared to a single server design?
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What technique can be used to resolve differences in the state of a file on different replicas?
What technique can be used to resolve differences in the state of a file on different replicas?
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Why does the replication model have a limitation in terms of scalability compared to partitioning?
Why does the replication model have a limitation in terms of scalability compared to partitioning?
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What file sharing semantics are typically used in a DFS to maintain acceptable performance?
What file sharing semantics are typically used in a DFS to maintain acceptable performance?
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In a single node Unix environment, why can Process B read 'abc' before the change is pushed to disk?
In a single node Unix environment, why can Process B read 'abc' before the change is pushed to disk?
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What is a limitation of using session semantics in DFS?
What is a limitation of using session semantics in DFS?
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Which mechanism in DFS helps correct conflicts periodically?
Which mechanism in DFS helps correct conflicts periodically?
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Why might the buffer cache prove not to be very useful in a scenario with high request-interleaving?
Why might the buffer cache prove not to be very useful in a scenario with high request-interleaving?
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What is the main drawback of using immutable file semantics in a distributed storage system?
What is the main drawback of using immutable file semantics in a distributed storage system?
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How do session semantics handle file updates in DFS when a client closes a file?
How do session semantics handle file updates in DFS when a client closes a file?
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Which type of operation allows a client to synchronize its state explicitly with the remote server in a DFS?
Which type of operation allows a client to synchronize its state explicitly with the remote server in a DFS?
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Why might periodic updates with time intervals lead to potential inconsistency in a distributed file system?
Why might periodic updates with time intervals lead to potential inconsistency in a distributed file system?
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"Leases" in DFS are analogous to which familiar concept in regular local file systems?
"Leases" in DFS are analogous to which familiar concept in regular local file systems?
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What is the main reason clients need to interact with the server in the discussed model?
What is the main reason clients need to interact with the server in the discussed model?
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Why does the text mention that the server is still in the loop in this model?
Why does the text mention that the server is still in the loop in this model?
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What makes a stateless file server unsuitable for practical models relying on caching?
What makes a stateless file server unsuitable for practical models relying on caching?
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Why is it mentioned that stateless servers prevent the use of caching?
Why is it mentioned that stateless servers prevent the use of caching?
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What is a significant advantage of stateless servers in terms of failure resilience?
What is a significant advantage of stateless servers in terms of failure resilience?
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Why does a stateful file server benefit from maintaining information about clients in the system?
Why does a stateful file server benefit from maintaining information about clients in the system?
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What role does state play in enabling a file server to provide locking mechanisms?
What role does state play in enabling a file server to provide locking mechanisms?
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Why is it stated that stateful servers are capable of supporting incremental operations?
Why is it stated that stateful servers are capable of supporting incremental operations?
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Which characteristic distinguishes a stateful server from a stateless server regarding client information?
Which characteristic distinguishes a stateful server from a stateless server regarding client information?
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What is one significant downside of stateless servers mentioned in the text?
What is one significant downside of stateless servers mentioned in the text?
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What is one of the challenges of a stateful server in a distributed file system?
What is one of the challenges of a stateful server in a distributed file system?
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In a stateless design, why must every single request be fully described?
In a stateless design, why must every single request be fully described?
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What does caching in a distributed file system allow clients to do?
What does caching in a distributed file system allow clients to do?
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Why is maintaining cache coherence challenging in a distributed file system?
Why is maintaining cache coherence challenging in a distributed file system?
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What is an effective way to trigger coherence mechanisms in a distributed file system according to the text?
What is an effective way to trigger coherence mechanisms in a distributed file system according to the text?
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Where can file caching be done within a distributed file system, based on the text?
Where can file caching be done within a distributed file system, based on the text?
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What problem arises when a client caches a portion of a file locally and another client modifies the same file?
What problem arises when a client caches a portion of a file locally and another client modifies the same file?
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Why might storing cache components on local storage devices benefit clients in a distributed file system?
Why might storing cache components on local storage devices benefit clients in a distributed file system?
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What does client-driven cache coherence mechanisms entail in a distributed file system?
What does client-driven cache coherence mechanisms entail in a distributed file system?
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Why is it important for clients to maintain local copies of portions of files in a distributed file system?
Why is it important for clients to maintain local copies of portions of files in a distributed file system?
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What type of guarantees could the file system provide in a distributed file system with transactional semantics?
What type of guarantees could the file system provide in a distributed file system with transactional semantics?
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In a server-driven mechanism for file sharing, what does session-semantics imply?
In a server-driven mechanism for file sharing, what does session-semantics imply?
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Why is it essential to understand the access pattern when designing a file system for a specific file sharing semantics?
Why is it essential to understand the access pattern when designing a file system for a specific file sharing semantics?
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What is the common reason for treating regular files and directories differently in a file system design?
What is the common reason for treating regular files and directories differently in a file system design?
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What is the purpose of providing transactional guarantees in a distributed file system?
What is the purpose of providing transactional guarantees in a distributed file system?
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How do session semantics impact overlapping sessions in a distributed file system?
How do session semantics impact overlapping sessions in a distributed file system?
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What is the focus of discussion in this lesson?
What is the focus of discussion in this lesson?
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Which research paper is discussed in this lesson?
Which research paper is discussed in this lesson?
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What is the purpose of discussing the Sprite Network File System?
What is the purpose of discussing the Sprite Network File System?
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What is a distributed file system likened to in this lesson?
What is a distributed file system likened to in this lesson?
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What are the two main requirements for both distributed file systems and storage facilities?
What are the two main requirements for both distributed file systems and storage facilities?
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What distribution models do distributed file systems support?
What distribution models do distributed file systems support?
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What is a potential downside of the Upload/Download model in a remote file service?
What is a potential downside of the Upload/Download model in a remote file service?
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What is a benefit of the True Remote File Access model in a remote file service?
What is a benefit of the True Remote File Access model in a remote file service?
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What is a limitation of the replicated model in a file system?
What is a limitation of the replicated model in a file system?
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What is an advantage of the partitioned model in a file system?
What is an advantage of the partitioned model in a file system?
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What is a potential downside of the True Remote File Access model?
What is a potential downside of the True Remote File Access model?
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What is a benefit of allowing clients to use their local resources for caching?
What is a benefit of allowing clients to use their local resources for caching?
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What is a limitation of the Upload/Download model in a remote file service?
What is a limitation of the Upload/Download model in a remote file service?
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What is a potential benefit of combining replication and partitioning in a file system?
What is a potential benefit of combining replication and partitioning in a file system?
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What is a potential disadvantage of the True Remote File Access model?
What is a potential disadvantage of the True Remote File Access model?
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What is a benefit of allowing clients to download some blocks of a file in a remote file service?
What is a benefit of allowing clients to download some blocks of a file in a remote file service?
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Study Notes
Distributed File Systems
- A distributed file system is a file system that can be organized in different ways:
- Clients and server on separate machines, with one file server.
- File server distributed on multiple machines, with file replication or partitioning.
Stateful vs Stateless File Server
- A stateless file server:
- Does not maintain information about clients or files.
- Each request is self-contained and has all necessary parameters.
- Suitable for extreme file service models (upload-download or true remote file access).
- Cannot be used for caching, which is an important performance optimization technique.
- Benefits: no resources consumed on the server side, resilient design, and easy recovery from failures.
- A stateful file server:
- Maintains information about clients and files (e.g., which clients have portions of a file cached).
- Allows data to be cached and guarantees consistency.
- Provides additional benefits, such as locking and incremental operations.
- Requires more complex mechanisms for recovery from failures.
Caching State in a DFS
- Caching is a general optimization technique in DFS:
- Clients can locally maintain portions of the state, perform some operations locally, and contact the server only when necessary.
- Caching can be done at the client's memory, local storage devices, or on the server-side in the buffer cache.
- Requires coherence mechanisms to maintain consistency between cached and server-side files.
- Different approaches include write-update, write-invalidate, and client-driven or server-driven coherence mechanisms.
File Sharing Semantics on a DFS
- File sharing semantics on a DFS differ from single-node Unix environments:
- Updates may not be immediately visible to other processes due to message latencies.
- DFS may sacrifice some consistency for performance and use relaxed file sharing semantics.
- Session semantics:
- Clients write back changes to the server when a file is closed.
- Clients check with the server for updates when a file is opened.
- Provides some consistency guarantees, but may not be suitable for concurrent file sharing.
- Periodic updates:
- Clients propagate updates to the server periodically.
- Server notifications and invalidations are also sent periodically.
- Establishes time bounds for potential inconsistencies.
Immutable File Semantics
- Immutable file semantics:
- Files cannot be modified once uploaded.
- Suitable for distributed storage facilities.
- Benefits: better performance, availability, and fault tolerance.
- Downsides: more complex write-update operations, and resolving consistency among replicas.
Distributed Storage Facilities
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Properties of distributed storage facilities:
- Accessed via well-defined interfaces.
- Update inventories to maintain consistent information.
- Can be configured in different ways (storage-only, storage and processing, specialized for different products).
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Relation to distributed file systems:
- Also accessed via high-level interfaces (Virtual File System).
- Maintain consistent state of files among clients.
- Can be implemented via different distribution models (replication, partitioning, or peer-to-peer nodes).### Distributed File Systems (DFS)
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DFS needs to provide transactional guarantees, allowing clients to specify a collection of files or operations as a single transaction.
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The file system should make guarantees that all changes are atomically committed and atomically visible.
DFS Data Structure
- In a server-driven mechanism with session-semantics, the per-file data structure should include:
- Information about current readers
- Information about current writers (potentially multiple)
- Version number to track changes and resolve conflicts
File vs Directory Service
- Understanding the workload (access pattern) is crucial for design and optimization considerations.
- File systems have different access patterns for regular files and directories, including:
- Locality
- Lifetime of files
- Size distribution
- Access frequency
- It is common to treat regular files and directories differently, e.g., adopting different semantics or using periodic updates with less frequent write-backs for regular files.
Replication and Partitioning
- The file server can be distributed via replication or partitioning.
- Replication involves replicating the file system onto multiple machines, with each machine holding an exact replica of all files.
- Partitioning involves dividing files across multiple machines, allowing for easier scaling.
Visual Metaphor
- Distributed file systems can be compared to distributed storage facilities, with a focus on maintaining consistent state.
- Both replicated and partitioned models can be used, or a combination of both.
- Partitioning allows for easier scaling, while replication provides consistency.
Remote File Service Extremes
- The Upload/Download model:
- Benefits: fast local operations, easy to implement
- Downsides: entire file needs to be downloaded, loss of file access control
- The True Remote File Access model:
- Benefits: server has full control, easier to ensure consistency
- Downsides: every operation incurs network latency, server overload
Remote File Service A Compromise
- A compromise between the two extremes is necessary, allowing clients to benefit from local caching and prefetching.
- This approach leads to lower latencies, reduced load on the server, and increased scalability.
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Description
Explore the basics of distributed file systems, focusing on design decisions and specifics of NFS. Learn about the research paper 'Caching in the Sprite Network File System' and understand the rationale behind design choices in the Sprite file system.