FlashTier: A Lightweight, Consistent and Durable Storage Cache 1 - - PowerPoint PPT Presentation

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FlashTier: A Lightweight, Consistent and Durable Storage Cache 1 - - PowerPoint PPT Presentation

Dec 01, 2023 131 likes •472 views

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SLIDE 1
  • FlashTier: A Lightweight, Consistent and

Durable Storage Cache

  • 1
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SLIDE 2
  • Introduction
  • Motivation
  • System Design
  • Evaluation
  • Related Work
  • Conclusion

Outline

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SLIDE 3

Flash

  • Flash’s price and performance are between DRAM

and disk.

  • write endurance:a single MLC flash cell can only

be erased 10,000 times. Introduction

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  • Flash’s 2 characteristics:
  • 1. Flash dose not support in-place writes.
  • 2. Flash devices use address mapping to translate

block addresses. Introduction

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  • Caches have at least 3 different behaviours that

distinguish them from general-purpose storage

  • 1. Data in a cache may be present elsewhere in the

system.

  • 2. A cache stores data from a separate address

space.

  • 3. A cache must ensure it never returns stale data.

Introduction

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SLIDE 6

OverView

  • FlashTier’s 3 features
  • 1. A unified address space
  • 2. Cache consistency guarantees
  • 3. Reduce the cost of garbage collection
  • Results :fewer memory usages、erase cycles、recovery

time.

Introduction

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  • Address Space Density.
  • Persistence and Cache Consistency.
  • Wear Management.

Motivation

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  • Address Space Density.

Motivate a change in how mapping information is stored Motivation

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  • Persistence and Cache Consistency.
  • large caches and poor disk performance result in

long cache warming periods.

  • require storing cache metadata
  • Wear Management.
  • garbage collection is often a contributor to wear.

Motivation

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  • FlashTier is a block-level caching system.
  • A cache manager interposes above the disk device

driver. System Design

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  • Unified Address Space
  • Consistent Cache Interface
  • Free Space Management
  • Cache Manager

System Design

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System Design

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  • Unified Address Space
  • Sparse Mapping

(google sparse hash map)

  • keep entire mapping in memory.

hybrid FTL 4KB Page 256KB Block

System Design

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  • Block State

SSC maintains: 1.the state of all flash blocks for GC. 2.usage statistics to guide wear-leveling and eviction store in out of band area (access by physical address

  • nly).

3.a reverse map for fast Address Translation

System Design

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  • Consistent Cache Interface
  • interface
  • 1. persist cached data across reboot or crash
  • 2. never return stale data because of an

inconsistent mapping. System Design

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System Design

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Choose victim (all clean | invalid) and erase only when remaining free blocks are insufficient

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SLIDE 17

System Design

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System Design

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SLIDE 19

System Design

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  • Consistent Cache Interface
  • Persistence

1.Logging 2.Checkpoints 3.Out-of-band writes. System Design

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  • Free Space Management

hybrid FTL data blocks 256KB, log blocks 4KB

  • silent eviction
  • policies:erase block with Min valid pages

1.SE-Util :create erased data block but not log block 2.SE-Merge:increase log block System Design

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  • Cache Manager Based on Facebook’s FlashCache

write-through: write-clean write-back: 1.write-dirty 2.maintain in-memory table of dirty blocks System Design

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  • Implementation
  • The Cache Manager(based on FlashCache)
  • An SSC Function Emulator(based on FlashSim)
  • An SSC timing simulator

2 Basic Configuration of the Simulator

  • 1. SSC(SE-Util)
  • 2. SSC-R(SE-Merge)

System Design

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  • What are the benefits of providing a sparse unified

cache address space for FlashTier?

  • What is the cost of providing cache consistency

and recovery guarantees in FlashTier?

  • What are the benefits of silent eviction for free

space management and write performance in FlashTier? Evaluation

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  • Emulation parameters & Workloads Characteristics

Evaluation

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  • System Comparison

1. Performance 2. Memory Consumption

Evaluation

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  • FlashTier Address Space Management

1. Device memory usage (native LBA_s -PA ,SSC LBA_d-PA) 2. Host memory usage

Evaluation

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  • FlashTier Consistency

1. Consistency Cost 2. Recovery Time

Evaluation

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  • FlashTier Consistency

1. Consistency Cost 2. Recovery Time

Evaluation

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  • FlashTier Silent Eviction

1. Garbage Collection 2. Cache Misses 3. Wear Management

Evaluation

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  • FlashTier Silent Eviction

Evaluation

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  • SSD Caches:

FlachCache ,dm-cache,bcache

  • Hybrid Systems:

FushionIO ,Synapse(OCZ)

  • Informed Caching
  • Storage Interfaces

Related Work

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  • Flash caching promises an inexpensive boost to

storage performance.

  • FlashTier provides memory-efficient address space

management, improved performance and cache consistency to quickly recover cached data following a crash.

  • reflection: Reduce GC in Common SSD Cache.

Conclusion

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