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Open Access Publications from the University of California

Scholarly Works (5 results)

  • Thesis
  • Peer Reviewed
UC Santa Cruz Electronic Theses and Dissertations (2014)

Non-volatile memory (NVRAM) storage devices are increasingly used in both consumer and enterprise systems, providing high performance and low energy consumption compared to hard drives. Unfortunately, an inflexible block interface and multiple I/O subsystems designed for slow hard drives make it difficult to utilize NVRAMs in a portable and efficient manner. For example, in the OS storage stack, I/O workloads are reshaped and throttled to generate a small number of concurrent I/O requests, though NVRAMs can handle much higher workloads, and unnecessary address mapping is performed in a file system. Using NVRAM as memory can be difficult with a block interface because of small reads and writes that are common in mem- ory workloads. At a device level, NVRAM devices need to perform a number of heuristics to attempt to recover filesystem-level semantics lost during the transmission through a block interface. As a result of these legacy interfaces, the current architecture is limited in achieving portability, efficiency, and extensibility, leaving behind more complicated problems, such as supporting heterogeneous NVRAM devices and utilizing device features.

This thesis proposes the use of the object-based storage model as a way of addressing the shortfalls of the current NVRAM architecture. More specifically, we show that the on- device NVRAM management layer can be as efficient as that of a native file system designed for a specific type of NVRAM while providing tightly coupled hardware optimizations and drop-in replacement for new types of NVRAMs. To explore the design flexibility given by this model, we investigate several data placement policies for flash memory exploiting the rich metadata coming from an object-interface. We also design an object-based byte-addressable NVRAM device to demonstrate that the object model allows more reliable, efficient NVRAM management by integrating its core data structures and a wear-leveling policy together. Our wear-leveling policy enables a low overhead, multi-granularity wear-level tracking for byte- addressable memories by exploiting the uniformity of a random function. We also investigate its extensibility and efficiency by designing Muninn, a object-based versioning key-value store for flash memory.

Realizing the object storage model requires changes in several subsystems of oper- ating systems and hardware components, but no further system changes will be required to support new types of NVRAM. Even with the current storage stack, we hypothesize that some of the features of this model can be adopted to better utilize device hardware and improve over- all efficiency of the storage system. To demonstrate these capabilities, we introduce Smart SSD, which pairs in-device processing with a powerful host system capable of handling data-oriented tasks without modifying operating system code. Our system is built on a real SATA-based SSD and extends the Hadoop MapReduce framework to support in-storage processing. Our experi- ments show that total energy consumption is reduced by 50% due to the low-power processing inside a Smart SSD. Moreover, a system with a Smart SSD can outperform host-side processing by a factor of two or three by efficiently utilizing internal parallelism when applications have light traffic to the device DRAM under the current architecture.

    Cover page: High-Performance, Reliable Object-Based NVRAM Devices
    • Article
    • Peer Reviewed
    UC Santa Cruz Previously Published Works (2014)
    While non-volatile memory (NVRAM) devices have the po-tential to alleviate the trade-off between performance, scal-ability, and energy in storage and memory subsystems, a block interface and storage subsystems designed for slow I/O devices make it difficult to efficiently exploit NVRAMs in a portable and extensible way. We propose an object-based storage model as a way of addressing the shortfalls of the current interfaces. Through the design of Muninn, an object-based versioning key-value store, we demonstrate that an in-device NVRAM manage-ment layer can be as efficient as that of NVRAM-aware key-value stores while not requiring host resources or host changes, and enabling tightly-coupled optimizations. Muninn is also designed to show that versioning can be added to a file system transparently with minimal host-side changes. As a flash key-value store, it achieves better life-time and low read/write amplification by eliminating internal data movements and per-object metadata updates using Bloom filters and hash functions. By doing so, it achieves as few as 1.5 flash page reads per look up and 0.26 flash page writes per insert on average with 50million 1KB key-value pairs without incurring data re-organization. This is close to the minimum number of flash accesses required to read and store the 1KB key-value pairs, thus increasing performance and lifetime of flash media.
      Cover page: Muninn: a Versioning Flash Key-Value Store Using an Object-based Storage Model
      • Article
      • Peer Reviewed
      UC Santa Cruz Previously Published Works (2012)
      Shingled Magnetic Recording technology is expected to play a major role in the next generation of hard disk drives. But it introduces some unique challenges to system software researchers and prototype hardware is not readily available for the broader research community. It is crucial to work on system software in parallel to hardware manufacturing, to ensure successful and effective adoption of this technology. In this work, we present a novel Shingled Write Disk (SWD) emulator that uses a hard disk utilizing traditional Perpendicular Magnetic Recording (PMR) and emulates a Shingled Write Disk on top of it. We implemented the emulator as a pseudo block device driver and evaluated the performance overhead incurred by employing the emulator. The emulator has a slight overhead which is only measurable during pure sequential reads and writes. The moment disk head movement comes into picture, due to any random access, the emulator overhead becomes so insignificant as to become immeasurable. © 2012 IEEE.
        Cover page: Emulating a Shingled Write Disk
        • Article
        • Peer Reviewed
        UC Santa Cruz Previously Published Works (2014)
        The ever-growing amount of data requires highly scalable storage solutions. The most flexible approach is to use storage pools that can be expanded and scaled down by adding or removing storage devices. To make this approach usable, it is necessary to provide a solution to locate data items in such a dynamic environment. This article presents and evaluates the Random Slicing strategy, which incorporates lessons learned from table-based, rule-based, and pseudo-randomized hashing strategies and is able to provide a simple and efficient strategy that scales up to handle exascale data. Random Slicing keeps a small table with information about previous storage system insert and remove operations, drastically reducing the required amount of randomness while delivering a perfect load distribution. © 2014 ACM.
          Cover page: Random Slicing: Efficient and Scalable Data Placement for Large-Scale Storage Systems
          • Article
          • Peer Reviewed
          UC Santa Cruz Previously Published Works (2011)
          In this paper, we present the design and performance evaluation of Oasis, an active storage framework for object-based storage systems that complies with the current T10 OSD standard. In contrast with previous work, Oasis has the following advantages. First, Oasis enables users to transparently process the OSD object and supports different processing granularity (from the single object to all the objects in the OSD) by extending the OSD object attribute page defined in the T10 OSD standard. Second, Oasis provides an easy and efficient way for users to manage the application functions in the OSD by using the existing OSD commands. Third, Oasis can authorize the execution of the application function in the OSD by enhancing the T10 OSD security protocol, allowing only authorized users to use the system. We evaluate the performance and scalability of our system implementation on Oasis by running three typical applications. The results indicate that active storage far outperforms the traditional object-based storage system in applications that filter data on the OSD. We also experiment with Java based applications and C based applications. Our experiments indicate that Java based applications may be bottlenecked for I/O-intensive applications, while for applications that do not heavily rely on the I/O operations, both Java based applications and C based applications achieve comparable performance. Our microbenchmarks indicate that Oasis implementation overhead is minimal compared to the Intel OSD reference implementation, between 1.2% to 5.9% for Read commands and 0.6% to 9.9% for Write commands. © 2011 IEEE.
            Cover page: Design and Evaluation of Oasis: An Active Storage Framework based on T10 OSD Standard
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