Online Migration For Geodistributed Storage Systems, Usenix Atc 2011

This paper investigates the work of migrating information betwixt information centers. Data needs to live moved from i centre to roughly other based on the access patterns, for example, the user may convey moved from East to West coast. The work is complicated past times the large size of information that needs to live moved, the requirement to perform the migration online without blocking access to whatever purpose of the information from anywhere, in addition to lastly that the information tin give notice live accessed/modified concurrently inwards dissimilar locations.

To address this problem, the newspaper proposes an overlay abstraction. The destination of the abstraction is to implement migration equally a service, therefore that the developer does non convey to bargain amongst the race weather that may effect piece migrating information inwards advertizing hoc ways. The analogy of overlay is a sail of transparencies. Remember the onetime days earlier powerpoint? The presenters used to impress the slides on transparencies, in addition to create animation past times overlaying i transparency over another. The overlay stance is similar. "Where it is clear, the overlay reveals the contents underneath; where it is written, the overlay overrides those contents." Basically, the stance is to correspond information equally stacked layers inwards dissimilar places. This enables migration of information inwards smaller units, in addition to the capability of having purpose of the information inwards i location in addition to the other parts inwards other locations.

Overlay is implemented much similar the (doubly) linked-list. Each overlay has ii pointers, i pointing to the overlay below, in addition to i pointing to the overlay above. Overlay insertion in addition to deletion are similar to those i would await from linked-list implementations. The overlay is designed such that every functioning is linearized past times the overlay construction fifty-fifty when the operations are submitted from whatever information center. Moreover, read in addition to write operations tin give notice live executed concurrently amongst the overlay construction operations in addition to amongst each other, at many clients without blocking.

To write information to an object the customer outset finds the highest overlay past times next the higher upward pointers starting from the based location. (Base location is learned from the directory service.) The information is written to this highest score overlay. To read an object, i time again the highest overlay is establish equally the outset step. If the information to live read is non there, in addition to therefore below pointers are followed until the information is reached.

The contribution of the newspaper is the abstraction that nicely separates policy score from the concurrency-safe execution of the actual migration operations. The newspaper presents several optimizations in addition to to a greater extent than use-cases for the overlay construction (such equally exploiting in-built replication for migration, multiway caching, in addition to divide overlays).

Share this post