PDL ABSTRACT

Comparing Performance of Different Cleaning Algorithms for SMR Disks

M.S. Thesis: Master of Science in Information Networking, April 2014..

Mukul Kumar Singh

Information Networking Institute
Carnegie Mellon University

http://www.pdl.cmu.edu/

Shingled Magnetic Recording (SMR) promises to sustain current growth in disk drive capacities with minimal change in the current disk drive technology. Shingling implies overlapping of tracks in a hard drive. Shingling would cause overwrites on down-track sectors with each sector write, hence new interfaces are being proposed to allow host software to exploit SMR with minimal change. An obvious interface is a Shingled Translation Layer which is akin to a Flash Translation Layer. Here the disk can completely hide the layer of remapping and background cleaning, but this comes at the cost of complexity in the disk processor and hard-to-predict performance changes. Other interfaces which enable the host application to handle shingling have been proposed as well. In a strict append model, the disk is divided into fixed sized bands and data is written to a particular band in a strict append order, with cleaning done by resetting the write cursor to the beginning of a band. Another promising interface, Caveat Scriptor, gives the host an address space of all possible sectors. In- order to handle shingling, this interface exposes two drive parameters to determine which sectors may or will not be damaged because of a certain write. These parame- ters are Drive No Overlap Range (DNOR) and Drive Isolation Distance (DID). This paper will explain these parameters, explain the design of a filesystem designed for this extreme interface, caveat scriptor, and compare the cleaning performance of a lesystem designed for the Caveat Scriptor interface to one designed for the Strict Append interface.

FULL PAPER: pdf

 

 

 

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