Efficient Recovery in Harp

Harp is a replicated Unix file system accessible via the VFS interface. It provides highly available and reliable storage for files and guarantees that file operations are executed atomically in spite of concurrency and failures. Replication enables Harp to safely trade disk accesses for network communication and thus to provide good performance both during normal operation and during recovery. In this position statement, we focus on the techniques Harp uses to achieve efficient recovery

Server Reintegration in a . . .

A distributed system is a collection of nodes connected by a network, an ideal platform to provide high reliable computing due to the redundancy supplied by a great number of nodes. Node faults and network connection faults can be masked reconfiguring the system. However, sequential faults, that affect multiple nodes can decrease the performance of the system affecting the system reliability and availability. To avoid this, failed nodes should be reintegrated as soon as possible. This paper details the problem of reintegration of failed nodes in a replicated UNIX file system. We built a prototype with the recovery protocols required by the reintegration procedure

Replication in the Harp File System

Harp uses the primary copy replication technique [1, 26, 27]. In this method, client calls are This paper describes the design and implementation of the directed to a single primary server, which communicates Harp file system. Harp is a replicated Unix file system with other backup servers and waits for them to respond accessible via the VFS interface. It provides highly avail- before replying to the client. The system masks failures by able and reliable storage for files and guarantees that file performing a failover algorithm in which an inaccessible operations are executed atomically in spite of concurrency server is removed from service. When a primary performs and failures. It uses a novel variation of the primary copy an operation, it must inform enough backups to guarantee replication technique that provides good performance be- that the effects of that operation will survive all subsequent cause it allows us to trade disk accesses for network com- failovers. munication. Harp is intended to be used within a file ser- Harp is one of the first implementations of a primary vice in a distributed network; in our current implemencopy scheme that runs on conventional hardware. It has tation, it is accessed via NFS. Preliminary performance some novel features that allow it to perform well. The key results indicate that Harp provides equal or better response performance issues are how to provide quick response for time and system capacity than an unreplicated implemen- user operations and how to provide good system capacity tation of NFS that uses Unix files directly. (roughly, the number of operations the system can handle in some time period while still providing good response time). Harp achieves good performance by recording the 1

Abstract Replication in the Harp File System

Harp uses the primary copy replication technique [1, 26, 27]. In this method, client calls are This paper describes the design and implementation of the Harp file system. Harp is a replicated Unix file system accessible via the VFS interface. It provides highly avail-able and reliable storage for files and guarantees that file operations are executed atomically in spite of concurrency and failures. It uses a novel variation of the primary copy replication technique that provides good performance be-cause it allows us to trade disk accesses for network communication. Harp is intended to be used within a file ser-vice in a distributed network; in our current implemen-tation, it is accessed via NFS. Preliminary performance results indicate that Harp provides equal or better response time and system capacity than an unreplicated implementation of NFS that uses Unix files directly. directed to a single primary server, which communicates with other backup servers and waits for them to respond before replying to the client. The system masks failures by performing a failover algorithm in which an inaccessible server is removed from service. When a primary performs an operation, it must inform enough backups to guarantee that the effects of that operation will survive all subsequent failovers. Harp is one of the first implementations of a primary copy scheme that runs on conventional hardware. It has some novel features that allow it to perform well. The key performance issues are how to provide quick response for user operations and how to provide good system capacity (roughly, the number of operations the system can handle in some time period while still providing good response 1