Concurrent updates on striped data streams in clustered server systems

Abstract

Data Striping is widely used and well-understood in Redundant Arrays of Independent Disks (RAID), whereby an array of disks is controlled by a single device controller. By striping and adding parity information, distribution of I/O load and fault tolerance can be assured. This study focuses the problem of update/read consistency of files that are striped among several nodes, e.g. in a clustered server for media streaming applications. Common RAID systems offer a single entry point so that a read operation delivers either the content before an update or the updated content. This property is not present when arbitrary nodes may access data stripes without a centralized access facility. Thus, coordination is necessary among updates and concurrent read operations. A common solution is to lock files or blocks that are currently being updated. We propose an alternative solution to ensure delivery of valid content during updates without locking blocks globally. This can be used for instance to update the original content of video servers, without the need of temporary copies and access limitations.