SSHDD

(ssshh.. we do it silently in the background)

Using SSD and HDD in a hybrid storage system

Files are moved between SSD and HDD without the user's knowledge with a goal to optimize file IO performance. The file movement is decided based on the access pattern and is dynamic in nature.

Algorithm

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• Maps file ID to physical file path
• SSD is always kept full
• Keep hot files on SSD
• Makes use of least recently used and most frequently used
• File swaps between SSD and HDD are made only when the priority differ by a threshold

Testing

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File access pattern data set : http://ita.ee.lbl.gov/html/contrib/WorldCup.html. All files in the access pattern data set are generated and the access pattern is simulated to study the performance gain in terms of time taken to read all files in the access pattern.

Dependencies

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1. libpqueue

git clone cd https://github.com/vy/libpqueue.git
cd libpqueue/src
gcc -c pqueue.c -o pqueue.o
ar rcs libpqueue.a pqueue.o

To run demo

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Requirements

1. Ubuntu 14.04 machine
2. USB pendrive

Important

To increase the number of messages that can be held in message queue

sudo sh -c 'echo 8000 > /proc/sys/fs/mqueue/msg_max'

Build

sh build.sh

Pendrive setup and config

1. Create a folder in pendrive, name of your choice
2. Open run.sh and change path of USB folder

Run

sh run.sh

This will run the 4 test cases as illustarted in the paper / presentation Time taken for each of the 4 tests can be verified from console prints

Results

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Increased the read throughput by approximately 100% when compared to a static allocation strategy

TODO

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• Add locking mechanism while modifying metadata