Computer Storage Systems
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Questions and Answers

How is non-volatile memory viewed in the context of computer systems?

  • As part of the I/O system (correct)
  • As a separate entity from the memory hierarchy
  • As part of the main memory bus
  • As a volatile memory component

    • What is a benefit of RAID 5 configuration?

  • It allows for faster data transfer rates
  • It provides a higher storage capacity
  • It offers better data redundancy (correct)
  • It is more cost-effective than other RAID configurations

    • What is the purpose of error-correcting codes in storage systems?

  • To prioritize data for faster access
  • To compress data for faster storage
  • To encrypt data for secure storage
  • To detect and correct data errors during transmission (correct)

    • How does parity work in data restoration?

    <p>By calculating the checksum of data blocks</p> Signup and view all the answers

    What is a characteristic of high-performance storage architectures?

    <p>They are designed to optimize data transfer rates and storage capacity</p> Signup and view all the answers

    What is a key feature of RAID 1 configuration?

    <p>It mirrors data to provide real-time duplication</p> Signup and view all the answers

    What is the primary performance bottleneck in the storage node?

    <p>Disks</p> Signup and view all the answers

    What is the approximately cost per IOPS of the storage system?

    <p>$7</p> Signup and view all the answers

    What is the formula to calculate availability?

    <p>MTTF / (MTTF + MTTR)</p> Signup and view all the answers

    What is the estimated mean time to fail of the rack?

    <p>531 hours</p> Signup and view all the answers

    What is the main advantage of using RAID 5 over RAID 1?

    <p>Increased storage capacity</p> Signup and view all the answers

    What is the purpose of error-correcting codes in storage systems?

    <p>To detect and correct data errors</p> Signup and view all the answers

    What is the primary benefit of using parity in storage systems?

    <p>Data restoration in case of failure</p> Signup and view all the answers

    What is the main characteristic of high-performance storage architectures?

    <p>High IOPS performance</p> Signup and view all the answers

    What is the estimated cost per terabyte of the storage system?

    <p>$1,000</p> Signup and view all the answers

    What is the main factor contributing to the high cost of the storage system?

    <p>Disks</p> Signup and view all the answers

    What is the main purpose of seek time in magnetic disks?

    <p>To position the arm over the proper track</p> Signup and view all the answers

    What is the average rotational latency (ARL) in magnetic disks?

    <p>8 ms to 2 ms</p> Signup and view all the answers

    What is the primary benefit of RAID systems?

    <p>To enhance the availability of data</p> Signup and view all the answers

    What is the main characteristic of RAID 0?

    <p>It is not redundant but more efficient</p> Signup and view all the answers

    What is the primary difference between reliability and availability?

    <p>Reliability is the probability of failure, while availability is the probability of unavailability</p> Signup and view all the answers

    What is the formula to calculate the average seek time (AST)?

    <p>Sum of the time for all possible seeks / Total number of possible seeks</p> Signup and view all the answers

    What is the primary benefit of increasing the recording density in magnetic disks?

    <p>To increase the storage capacity</p> Signup and view all the answers

    What is the formula to calculate the disk access time (DAT)?

    <p>Seek time + Rotational latency + Transfer time + Controller time + Queuing delay</p> Signup and view all the answers

    What is the primary advantage of using error-correcting codes in magnetic disks?

    <p>To detect and correct errors</p> Signup and view all the answers

    What is the main purpose of parity in RAID systems?

    <p>To restore data in case of failure</p> Signup and view all the answers

    Study Notes

    Storage

    • Non-volatile memory can be viewed as part of the memory hierarchy system or I/O system
    • Characteristics of storage include: seek time, rotational latency, and transfer time
    • Seek time: 5-12 ms, with actual time being 25-33% of reported time due to locality of disk references
    • Rotational latency: average 8 ms to 2 ms, depending on RPM (3,600 to 15,000) and disk diameter (1.0 to 3.5 inches)
    • Transfer time depends on transfer size per sector, rotation speed, and recording density
    • Magnetic disks evolution has led to increased density, reduced prices, and increased RPM

    Magnetic Disks Performance

    • Average seek time (AST) is the sum of time for all possible seeks divided by the total number of possible seeks
    • Rotational latency (ARL) is half the rotation period, with common values being 5,400 and 7,200 RPM
    • Transfer time depends on transfer size, rotation speed, and recording density
    • Disk access time (DAT) is the sum of seek time, rotational latency, transfer time, controller time, and queuing delay

    RAID Systems

    • RAID (Redundant Array of Independent Disks) systems are designed for reliability and availability
    • Characteristics: multiple simultaneous accesses, data stripping, and mirroring to increase availability
    • Reliability vs availability: more disks mean greater fail probability, but failures do not necessarily lead to unavailability
    • RAID levels summary: level 0 (not redundant, but efficient), level 1 (mirroring), and level 3 (striping with parity)

    I/O Servers - Clusters

    • Performance evaluation: the network switch can be the bottleneck if it cannot support the required bandwidth
    • Cost: disks represent almost 70% of the total cost, with a cost per terabyte of almost $1,000 and cost per IOPS of about $7
    • Dependability: mean time to failure (MTTF), mean time to repair (MTTR), and mean time between failures (MTBF)
    • Availability: MTTF / (MTTF + MTTR)

    I/O Servers - Clusters (cont.)

    • Dependability: resulting mean time to fail of the rack, with assumptions about MTTF for various components (CPU, memory, enclosure, disks, controllers, switches, power supplies, and fans)
    • Calculation of failure rate and MTTF for the rack

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    Description

    This quiz covers the characteristics of non-volatile memory, including seek time, rotational latency, and transfer time, as part of the memory hierarchy and I/O systems.

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