Storage Class Memories

Description

We are investigating the use of Storage Class Memories (SCMs) to build faster, more reliable storage systems. SCMs are non-volatile memory technologies that have become popular in enterprise systems as well as embedded and mobile systems. Flash memory can be considered as an early version of SCM. Phase-Change RAM (PRAM) is one of the several memory technologies that promise speed and density comparable to DRAM. Though providing low power consumption, fast random I/O performance and shock resistance, replacing hard drives with SCMs in the current systems often incurs non-trivial changes and performance degradation due to the limitation of block-based interface.

If file systems have a direct access to the raw flash memory, it can avoid using a block-based interface, and thus utilizing the flash device efficiently. We have developed a high performance and reliabile flash file system called RCFFS. Our file system has increased reliability by integrating two-level parities and algebraic signature while not sacrificing both performance and space efficiency.

However, dealing with SCM characteristics on a host side may not be an ideal approach, because it would make the file system design complicated, and the SCM device has better knowledge about the hardware such as internal bandwidth and channels. Current SSD offers a similar functionality, but its performance and design flexibility limited by the existing components designed for hard drives. We have introduced the use of an object-based interface for SCM devices. It can alleviate the problems of multiple translation layers and sub-optimal performance of SSDs by offloading the block management layer to the device and providing a rich interface between a host and a device. We have developed a prototype of an object-based file system and an object-based flash device to show the effects of this model.

Due to a flexible object interface and a powerful processing capability of SCM devices, object-based storage devices can provide additional functionality beyond basic read and write operations. As a prototype of this type of devices, we have worked with researchers at Samsung Electronics to design a Smart SSD model, which adds a search capability and an object-based communication processing to the existing SSD firmware, and uses MapReduce style APIs as an application interface. We have explored the benefits and limitations using in-storage processing with the current SSD architecture. Our measurement shows that while the limitations of the internal architecture of a SSD limits the range of applications, Smart SSDs can save 50% of the total energy while providing comparable or faster search performance due to the high internal bandwidth and no host system resource usage.

Status

Object devices can be thought of as key-value stores that take a fixed-length key and a variable-length value. Beyond the design of storage devices for file systems, we are currently looking into the design of object-based key-value stores using flash memory or byte-addressable SCMs. Our goal is to provide low-latency reads and facilitate high-bandwidth writes while handling wear-leveling and SCM-characteristics internally so the OSDs can be simultaneously used as both memory and storage device.

Useful Links

Here are some links relevant to storage class memories.

• Samsung announcement about phase-change RAM, a replacement for flash

Publications

2013

• Yangwook Kang, Yang-suk Kee, Ethan L. Miller, Chanik Park, Enabling Cost-effective Data Processing with Smart SSD, the 29th IEEE Symposium on Massive Storage Systems and Technologies (MSST 13), May 2013.

2011

• Yangwook Kang, Jingpei Yang, Ethan L. Miller, Object-based SCM: An Efficient Interface for Storage Class Memories, Proceedings of the 27th IEEE Conference on Mass Storage Systems and Technologies: Research Track (MSST 2011), May 2011.
• Nate Edel, MRAMFS: A Compressing File System for Byte-Addressable Non-Volatile RAM, Technical Report UCSC-SSRC-11-02, March 2011.

2010

• Ignacio Corderi, Thomas Schwarz, Ahmed Amer, Darrell D. E. Long, Jehan-François Pâris, Self-Adjusting Two-Failure Tolerant Disk Arrays, Proceedings of the 5th International Workshop on Petascale Data Storage (PDSW10), held in conjunction with SC2010, November 2010.
• Sara Chaarawi, Jehan-François Pâris, Ahmed Amer, Thomas Schwarz, Darrell D. E. Long, Using a Shared Storage Class Memory Device to Improve the Reliability of RAID Arrays, Proceedings of the 5th International Workshop on Petascale Data Storage (PDSW10), held in conjunction with SC2010, November 2010.
• Yangwook Kang, Jingpei Yang, Ethan L. Miller, Efficient Storage Management for Object-based Flash Memory, Proceedings of the 18th Annual Meeting of the IEEE International Symposium on Modeling, Analysis and Simulation of Computer and Telecommunication Systems (MASCOTS 2010), August 2010.

2009

• Yangwook Kang, Ethan L. Miller, Adding Aggressive Error Correction to a High-Performance Flash File System, Proceedings of the 9th ACM/IEEE Conference on Embedded Software (EMSOFT '09), October 2009.
• Kevin Greenan, Darrell D. E. Long, Ethan L. Miller, Thomas Schwarz, Avani Wildani, Building Flexible, Fault-Tolerant Flash-based Storage Systems, Proceedings of the Fifth Workshop on Hot Topics in System Dependability (HotDep 2009), June 2009.
• Jehan-François Pâris, Ahmed Amer, Darrell D. E. Long, Using storage class memories to increase the reliability of two-dimensional RAID arrays, Technical Report UCSC-SSRC-09-04, April 2009.

2008

• Jehan-François Pâris, Darrell D. E. Long, Thomas Schwarz, Ensuring Data Survival on Solid-State Storage Devices, Proceedings of the 1st International Workshop on Storage and I/O Virtualization, Performance, Energy, Evaluation and Dependability, February 2008.

2007

• Sasha Ames, LiFSBrowse: A Visual, User Environment for the Linking File System, Technical Report UCSC-SSRC-07-08, August 2007.
• Kevin Greenan, Ethan L. Miller, PRIMS : Making NVRAM Suitable for Extremely Reliable Storage, short paper in Proceedings of the 3rd Workshop on Hot Topics in System Dependability (HotDep '07), June 2007.
• Timothy Bisson, Scott A. Brandt, Flushing Policies for NVCache Enabled Hard Disks, Technical Report UCSC-SSRC-07-04, May 2007.
• Timothy Bisson, Scott A. Brandt, Reducing Hybrid Disk Write Latency with Flash-Backed I/O Requests, Technical Report UCSC-SSRC-07-03, May 2007.
• Timothy Bisson, Scott A. Brandt, Darrell D. E. Long, A Hybrid Disk-Aware Spin-Down Algorithm with I/O Subsystem Support, Proceedings of the International Performance Conference on Computers and Communication (IPCCC '07), April 2007. Won Best Paper Award.
• Carlos Maltzahn, Nikhil Bobb, Mark W. Storer, Damian Eads, Scott A. Brandt, Ethan L. Miller, Graffiti: A Framework for Testing Collaborative Distributed Metadata, Proceedings in Informatics 21, March 2007, pages 97–111.
• Mark W. Storer, Graffiti Server - Design and Implementation, Technical Report UCSC-SSRC-07-02, January 2007.

2006

• Kevin Greenan, Ethan L. Miller, Reliability Mechanisms for File Systems Using Non-Volatile Memory as a Metadata Store, Proceedings of the 6th ACM & IEEE Conference on Embedded Software (EMSOFT '06), October 2006, pages 178-187.
• Timothy Bisson, Scott A. Brandt, Darrell D. E. Long, NVCache: Increasing the effectiveness of disk spin-down algorithms with caching, Proceedings of the 14th International Symposium on Modeling, Analysis, and Simulation of Computer and Telecommunication Systems (MASCOTS 2006), September 2006.
• Sasha Ames, Nikhil Bobb, Kevin Greenan, Owen Hofmann, Mark W. Storer, Carlos Maltzahn, Ethan L. Miller, Scott A. Brandt, LiFS: An attribute-rich file system for storage class memories, Proceedings of the 23rd IEEE / 14th NASA Goddard Conference on Mass Storage Systems and Technologies, May 2006.
• Nikhil Bobb, Damian Eads, Mark W. Storer, Scott A. Brandt, Carlos Maltzahn, Ethan L. Miller, Graffiti: A framework for testing collaborative distributed metadata, Proceedings of the 7th International Workshop on Distributed Data and Structures (WDAS 2006), January 2006.

2005

• Sasha Ames, Nikhil Bobb, Scott A. Brandt, Adam Hiatt, Carlos Maltzahn, Ethan L. Miller, Alisa Neeman, Deepa Tuteja, Richer file system metadata using links and attributes, Proceedings of the 22nd IEEE / 13th NASA Goddard Conference on Mass Storage Systems and Technologies, April 2005.
• Timothy Bisson, Scott A. Brandt, Reducing Energy Consumption with a Non-Volatile Storage Cache, International Workshop on Software Support for Portable Storage (IWSSPS) held in conjunction with the IEEE Real-Time and Embedded Systems and Applications Symposium (RTAS 2005), March 2005.

2004

• Nate Edel, Deepa Tuteja, Ethan L. Miller, Scott A. Brandt, MRAMFS: a compressing file system for non-volatile RAM, Proceedings of the 12th International Symposium on Modeling, Analysis, and Simulation of Computer and Telecommunication Systems (MASCOTS '04), October 2004, pages 596-603.
• Nate Edel, Karl Brandt, Ethan L. Miller, Scott A. Brandt, Measuring the compressibility of metadata and small files for disk/nvram hybrid storage systems., Proceedings of the 2004 International Symposium on Performance Evaluation of Computer and Telecommunication Systems (SPECTS '04), July 2004.

2003

• Nate Edel, Karl Brandt, Ethan L. Miller, Scott A. Brandt, Measuring the compressibility of metadata and small files for disk/NVRAM hybrid storage systems, Technical Report UCSC-CRL-03-04, Storage Systems Research Center, University of California, July 2003.

2002

• Alicja Szczurowska, MRAM–preliminary analysis for file system design, Master's thesis, University of California, Santa Cruz, March 2002, March 2002.

2001

• Ethan L. Miller, Scott A. Brandt, Darrell D. E. Long, HeRMES: High-Performance Reliable MRAM-Enabled Storage, Proceedings of the 8th IEEE Workshop on Hot Topics in Operating Systems (HotOS-VIII), May 2001, pages 83-87.