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Storage Architecture. CE202 December 2, 2003 David Pease. Faster. Smaller. Higher. Cache. RAM. Capacity. Speed. Cost. Disk. Optical. Tape. Slower. Larger. Lower. Hierarchy of Storage. Storage System Components. Application I/O Library File System Device Driver

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Storage architecture

Storage Architecture

CE202

December 2, 2003

David Pease


Hierarchy of storage

Faster

Smaller

Higher

Cache

RAM

Capacity

Speed

Cost

Disk

Optical

Tape

Slower

Larger

Lower

Hierarchy of Storage


Storage system components
Storage System Components

  • Application

  • I/O Library

  • File System

  • Device Driver

  • Host Bus Adapter

  • Interconnect

  • Storage Controller

  • Devices I/O Context



Disk drives
Disk Drives

  • “Workhorse” of modern storage systems

  • Capacity increasing, raw price dropping

    • can buy 1TB for only $1000!

    • bandwidth not keeping pace

    • reliability is actually decreasing

      • massive systems can mean even lower availability

  • Majority of cost of ownership in administration, not purchase price

    • backup, configuration, failure recovery


Disk architecture
Disk Architecture

spindle

cylinder

sector

track

platters

arms with

read/write

heads

rotation






RAID

  • Redundant Arrays of Inexpensive Disks

  • Two orthogonal concepts:

    • data striping for performance

    • redundancy for reliability

  • Striped arrays can increase performance, but at the cost of reliability (next page)

    • redundancy can give arrays better reliability than an individual disk



One month trace of hardware failures
One-month Trace of Hardware Failures

Trace collected from the Internet Archive (March 2003)

(thanks Kelly Gottlib)

-- Over 100 terabytes of compressed data

-- 30 disk failures out of total 70 hardware problems



Raid levels1
RAID Levels

0

1

2

3

4

5

6


Raid 4x small write penalty
RAID: 4x Small Write Penalty

small data write

xor

3

4

1

2

5


Log structured file systems
Log-Structured File Systems

  • Based on assumption that disk traffic will become dominated by writes

  • Always writes disk data sequentially, into next available location on disk

    • no seeks on write

  • Eliminates problem of 4x write penalty

    • all writes are “new”, no need to read old data or parity

  • However, almost no examples in industry file systems



Tape media
Tape Media

  • Inherently sequential

    • long time to first byte

    • no random I/O

  • Subject to mechanical stress

    • number of read-write cycles lower than disk

  • Problems as an archival medium:

    • readers go away after some years

      • most rapidly in recent years

    • tapes (with data) remain in a salt mine


Tape media1
Tape Media

  • Density will always trail that of disk

    • Tape stretches, more difficult to get higher density

  • Alignment also an issue

    • once it’s past the head, it’s gone

    • more conservative techniques required

  • Bottom line: mechanical engineering issues for tape are the difficult ones


Optical
Optical

  • CD, CD-R/RW, DVD, DVD-R/RW

    • Capacities:

      • CD: ~700MB (huge 20 years ago!)

      • DVD:

        • single sided, single layer: 5GB

        • single sided, double layer: 9GB

        • double sided, single layer: 10GB

        • double sided, double layer: 18GB

      • Size of cell limited by wavelength of light

        • current lasers are red

        • blue lasers are under development, then UV, ...


Optical1
Optical

  • Magneto-optical (HAMR)

    • heat from laser makes changing direction of magnetization easier (so cell is smaller)


MEMS

  • MicroElectroMechanical Systems

    • 6-10 times faster than disk

    • cost and capacity issues


Magnetic ram mram
Magnetic RAM (MRAM)

  • Stores each bit in a magnetic cell rather than a capacitor or flip-flop

    • data is persistent

  • Can be read and written very quickly

    • Read and write times 0.5 – 10 µs or less

    • Individual bits are writeable (no block erase)

  • Density & cost comparable to DRAM

    • may require density/speed tradeoffs

    • denser MRAM may have to run slower because of heat dissipation on writes


Magnetic ram mram1
Magnetic RAM (MRAM)

  • Several companies have announced partnerships to produce products ~2003

  • Ideas for use of MRAM in storage:

    • Persistent cache

      • Hot data in MRAM, cold data to disk

      • No need to flush write cache to avoid data loss

    • HeRMES

      • all metadata in MRAM

      • enough file data in MRAM to hide disk latency for first access to a file


Peripheral buses
Peripheral Buses

  • SCSI

  • IDE/ATA

  • HIPPI (High Performance Parallel Intf.)

  • IEEE 1394 (FireWire)

  • FibreChannel (FCP)

  • IP (e.g., iSCSI)

  • InfiniBand

  • Serial ATA


Peripheral buses1
Peripheral Buses

  • Parallel

    • SCSI, most printers, IBM Channels

    • 1 or more bytes per clock

    • Skew problems at high speeds

  • Serial

    • FC, RS232, IEEE1394 (FireWire)

    • 1 bit per clock, self clocking

    • can be run at much higher speeds than parallel bus


Networked storage
Networked Storage

  • Storage attached by general-purpose or dedicated network (e.g., FibreChannel)

  • Motivations:

    • homogenous and heterogeneous file sharing

    • centralized administration

    • better resource utilization (shared storage resources, pooling)

  • Dedicated Networks:

    • Fibre-Channel: FCP (SCSI over FC)

    • iSCSI: SCSI over IP

    • InfiniBand


Networked storage1
Networked Storage

  • Can mean many things:

    • NAS (Network-Attached Storage): file server appliances serving NFS and/or CIFS (for example, Network Appliance)

    • NASD (Network-Attached Secure Disk): intelligent, network-attached drives w/ security features (also, Network-Attached Storage Device)

    • SAN (Storage Area Network): network for attaching disks and computers, usually dedicated only to storage operations

      • OBSD (Object-Based Storage Device): similar to NASD


Solaris

Win2K

Linux

AIX

IFS w/cache

IFS w/cache

IFS w/cache

IFS w/cache

A SAN File System

NFS

CIFS

FTP

HTTP

Control Network (IP)

Meta-data

Server

Meta-data

Server

Meta-

data

SAN

Meta-data

Server

data

Security

assists

Storage

Management

Server

HSM &

Backup

Data

Data


Additional reading
Additional Reading

  • Hennessy & Patterson: Chapter 6

  • Chen, Lee, Gibson, Katz, & Patterson: RAID: high performance, reliable secondary storage. ACM Computing Surveys 26, June 1994, 145-185

  • Rosenblum & Ousterhout: The design and implementation of a log-structured file system. ACM Transactions on Computer Systems, Feb. 1992, 26-52

  • Gibson, Nagle, et al.: A cost-effective, high-bandwidth storage architecture. Proceedings of the Eight Conference on Architectural Support for Programming Languages and Operating Systems, 1998

  • http://www.almaden.ibm.com/cs/storagesystems/stortank/


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