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Presented byIftikhar Alam  Ms 2nd semester   Supervised byProf: Dr.Shah Khusro
   Abstract   Introduction   Overview of disk drives   Performance overview   Disk controller   Reliability   Energ...
   This article explain:   Importance of energy efficiency in designing    disk drive storage systems.   Hard drive des...
   Disk drive is         ◦ most important storage , offers high performance         ◦ large capacity ,high reliability   ...
   Magnetic recording technology       Has two mile stones   Longitudinal recording and Perpendicular recording.Hard di...
   Traditional longitudinal recording technology has    successfully achieved 100% growth of areal density (AD)   AD: is...
   Superparamagnetic effect (shrinking volume of    magnetic grains) poses a serious challenge for    further increases o...
   But, the grain size cannot be decreased much below a    diameter of ten nanometers. Using fewer magnetic grains in a  ...
Hard disks mainly consists of platters, spindle, disk arm, disk head,motor, controller, etc.The platters spin at a constan...
   Disk access time:       Taccess = Tseek + Trotate + Ttransfer    ◦ Seek Time. Time it takes to locate a particular pi...
   Data Transfer Time    ◦ Consists of two parts          External data transfer: Rate between memory and           disk...
   Geometric features:    ◦ Outer tracks on disk platters are much larger than the inner      tracks. Modern disk drives ...
   A disk controller contains   Storage interface offers a standard protocol       (e.g., IDE, SCSI, FC, SATA, etc.)  ...
   Disk cache        Temporarily holding data        Principles of data locality to improve hit ratio        All moder...
   Disk Scheduler       Queue the incoming requests.   Scheduling algorithms       First Come First Served (FCFS)     ...
Spin down = Idle to standby                                       Spin up = standby to activeTable I. The Major Characteri...
   Energy Conservation Methods    ◦ 1. Timeout strategy         Once a disk drive is idle ,the disk is spun         down ...
   Performance of disk drives has been    experiencing 40% growth per year, a number    of constraints pose challenges to...
   Disk cache can be improve the performance of disk drives by    avoiding slow mechanical latency(measured in millisecon...
   Increasing the RPM can improve disk drive    performance significantly.   Unfortunately, disk drives rotating at spee...
   Power states transition is not applicable to the server disk drives.   Dynamic Rotations Per Minute (DRPM)is proposed...
   Flash Memory      Nonvolatile,electrically erased and reprogrammed      small physical size ,lower power consumption...
   Promising Storage Media    ◦ Flash memory    ◦ Magnetic Random Access Memory (MRAM)       Combines a magnetic device ...
   Phase-change Random Access Memory    (PRAM)    ◦ Mature technology than MRAM or MEMS.    ◦ Samsung introduced a 512Mb ...
   Anatomy of Hybrid Disk.    ◦ DRAM are nanosecond devices.    ◦ NAND chips are microsecond devices.    ◦ NAND flash mem...
   The challenges (e.g., endurance cycles, erase before write,    etc.) presented by NAND flash memory indicate that the ...
   Disk has to stay in the low-power state for a    sufficiently long period of time which save the    energy . This ener...
   In the past 50 years, disk drive architecture has    remained largely unchanged.   They have reached a turning point ...
Thanks
What is the future of disk drives?
What is the future of disk drives?
What is the future of disk drives?
What is the future of disk drives?
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What is the future of disk drives?

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What is the future of disk drives?

  1. 1. Presented byIftikhar Alam Ms 2nd semester Supervised byProf: Dr.Shah Khusro
  2. 2.  Abstract Introduction Overview of disk drives Performance overview Disk controller Reliability Energy consumption overview Design constraints New disk drive architectures New storage media and storage devices Discussions Conclusions
  3. 3.  This article explain: Importance of energy efficiency in designing disk drive storage systems. Hard drive design have reached a turning point at which they have to be reborn in order to maintain high reliability and energy efficiency. The evaluation of disk drive over 5 decads.
  4. 4.  Disk drive is ◦ most important storage , offers high performance ◦ large capacity ,high reliability  Since IBM 1301 disk drive was announced in 1961, disk drives have experienced dramatic development to meet capacity, performance, and other capability requirements. The 1301 stored 28 million characters on a single module IBM 1301 disk drive
  5. 5.  Magnetic recording technology  Has two mile stones Longitudinal recording and Perpendicular recording.Hard disk technology with longitudinalrecording has an estimated limit of 100 to 200 gigabit per square inch. Perpendicular recording was usedin 2005 for hard disks.Perpendicular allow information densities of up to around 1 Tbit/sq. inch (1000 Gbit/sq. inch).In August 2010 drives withdensities of 667Gb/in2 were available commercially.
  6. 6.  Traditional longitudinal recording technology has successfully achieved 100% growth of areal density (AD) AD: is a measure of the number of bits that can be stored in a unit of area. It is usually expressed in bits per square inch (BPSI). Areal density is computed as the product of two density measures. ◦ Track Density(TPI): How many tracks can be placed down in inch of radius on the platters. ◦ Linear or Recording Density(BPI): How tightly the bits are packed within a length of track. If in a given inch of a track we can record 200,000 bits of information, then the linear density for that track is 200,000 bits per inch per track (BPI).
  7. 7.  Superparamagnetic effect (shrinking volume of magnetic grains) poses a serious challenge for further increases of the AD. The reason is that each bit cell in a track is composed of multiple magnetic grains. Bit-cell composed of magnetic grains 50-100 grains/bit
  8. 8.  But, the grain size cannot be decreased much below a diameter of ten nanometers. Using fewer magnetic grains in a bit cell requires more complicated error correcting codes. The growth mainly depends on the improvement of Revolutions Per Minute (RPM), magnetic recording technology, the size of the on-board cache, along with some reductions in the seek time [Hitachi 2009]. Trends of recent years imply that flash memory could be a good candidate for bridging the performance gap. However flash-based storage devices are still expensive, and their characteristics such as write endurance (each memory cell has a limited number of times that it can be erased before the memory cell fails ) and erase before write are still challenging problems.
  9. 9. Hard disks mainly consists of platters, spindle, disk arm, disk head,motor, controller, etc.The platters spin at a constant rate called RPM. The data is recordedmagnetically in concentric tracks on the platters.
  10. 10.  Disk access time:  Taccess = Tseek + Trotate + Ttransfer ◦ Seek Time. Time it takes to locate a particular piece of information . ◦ Rotational Latency: when the disk head arrives at the target track, it must wait for first sectore before it begins to transfer data. ◦ Data Transfer Time. Data transfer time is the amount of data divided by the data transfer rate.
  11. 11.  Data Transfer Time ◦ Consists of two parts  External data transfer: Rate between memory and disk cache  Internal data transfer :Rate between disk cache and disk storage media  Internal data transfer is also called Internal Data Rate (IDR).  Expressed in MB/s  IDR is much lower than the external data rate because reading or writing on disk plate is time consuming.
  12. 12.  Geometric features: ◦ Outer tracks on disk platters are much larger than the inner tracks. Modern disk drives employ a technique called ZBR. ◦ Zone Bit Recording (ZBR) is used by disk drives to store more sectors per track on outer tracks than on inner tracks. ◦ ZBR results in a much smaller data transfer time of outer zones than that of inner zones.
  13. 13.  A disk controller contains Storage interface offers a standard protocol  (e.g., IDE, SCSI, FC, SATA, etc.) Disk sequencer  Manages the data transfer between storage interface and data buffer. ECC  Responsible for error checking. Servo control  Detects the current position of the disk head Microprocessor  Overall control of disk drive. Disk cache  Temporary storage.
  14. 14.  Disk cache  Temporarily holding data  Principles of data locality to improve hit ratio  All modern disk drives contain a small amount of on-board cache (RAM) to speed up access to data on a disk drive. Cache replacement algorithms(Already done in OS) Random Replacement(RR)  RR replaces cache lines by randomly selecting a cache line  very fast,  requires no extra storage  easiest one to implement  performs poorly(a page that will used in near future may be swapped) Least Frequently Used (LFU)  Which have been used least frequently are evicted.  Recently active but currently cold cache lines  Increases the miss ratio and reduces the cache performance. Least Recently Used (LRU) ◦ Evicts those cache lines used least in the recent past on the assumption that they will not be used in the near future
  15. 15.  Disk Scheduler  Queue the incoming requests. Scheduling algorithms  First Come First Served (FCFS)  Shortest Seek Time First (SSTF)  SCAN algorithm Reliability Disk drive consists of one or more platters rotating on a common spindle Spindle motor is adopted to spin the platters and maintain the RPM. They may fail due to various component failures (e.g., disk head, media, firmware, etc.) The environmental factors, including temperature, humidity, vibration, etc all have impacts on the failure of disk drives
  16. 16. Spin down = Idle to standby Spin up = standby to activeTable I. The Major Characteristics of Five Different Disk Drives
  17. 17.  Energy Conservation Methods ◦ 1. Timeout strategy Once a disk drive is idle ,the disk is spun down in an effort to save energy. Widely used. 2. Application-aware power management Requires modifying existing applications, which makes it impractical. 3. Compiler-driven method for disk power management has been suggested . 4. Bucket method : Extending the idle length so energy is be conserved.
  18. 18.  Performance of disk drives has been experiencing 40% growth per year, a number of constraints pose challenges to continue the 40% growth rate. The growth of AD results in decreased seek time and increased IDR. The perpendicular recording technology will also reach its limits soon, and new technologies will be required [Perpendicular Recording2009].
  19. 19.  Disk cache can be improve the performance of disk drives by avoiding slow mechanical latency(measured in milliseconds, include both seek time and rotational latency). Accessing a byte of data in cache is much faster than accessing a byte on the rotating magnetic disk media. However, studies have indicated that if the disk cache size grows beyond its limits may cause performance penalty. Heat generated by certain actions within the disk drive which effect reliable operation.  High temperature = Head crashes
  20. 20.  Increasing the RPM can improve disk drive performance significantly. Unfortunately, disk drives rotating at speeds exceeding 20, 000 RPM have been researched but not commercialized due to heat generation, power consumption, noise, vibration. Therefore, it is a big challenge to design new disk drive architecture which could further advance disk performance.
  21. 21.  Power states transition is not applicable to the server disk drives. Dynamic Rotations Per Minute (DRPM)is proposed for power management in server disk arrays. The DRPM technique dynamically modulates the rotational speed of disk drives so that the disk can serve requests at different RPMs. Multispeed disk approach is also suggested to conserve energy. EED [Deng et al. 2008b] is an energy-efficient disk drive architecture by extending the length of idle intervals . A disk drive including two or more spindles each carrying one or more platters was introduced. Hard Disk Drive with Multiple Spindles [2011].
  22. 22.  Flash Memory  Nonvolatile,electrically erased and reprogrammed  small physical size ,lower power consumption  high performance ,Used in digital cameras, MP3 players, mobile phones, etc. Two major types of flash memory ◦ NOR: Byte accessible, mainly used for EEPROM replacement ◦ NAND: Block accessible ,faster erasing and write times, higher data density. Writing is done in a unit of one page , erasing is done in blocks. ◦ NAND flash memory can play two roles  As an extension to RAM, and a layer between RAM and traditional disk drives.  Replacing traditional disk drives as a new block storage media.
  23. 23.  Promising Storage Media ◦ Flash memory ◦ Magnetic Random Access Memory (MRAM)  Combines a magnetic device with standard silicon- based microelectronics to obtain the combined attributes of nonvolatility, high performance, fast programming. ◦ MicroElectroMechanical System (MEMS)  MEMS-based storage is a nonvolatile storage technology that merges magnetic recording material with thousands of probe-based recording heads to provide online storage [Schlosser et al. 2000]. However, both MRAM and MEMS are still in their infant phase of development.
  24. 24.  Phase-change Random Access Memory (PRAM) ◦ Mature technology than MRAM or MEMS. ◦ Samsung introduced a 512Mb PRAM ◦ Expected to be the main memory device and to replace the high density NOR flash within the next decade [Samsung 2009d]. PRAM can rewrite data without having to first erase data previously accumulated, it is effectively 30 times faster than conventional flash memory. Hybrid Disk ◦ Performance Gap within Disk Drives  Disk drives normally use conventional main memory (SDRAM) as disk cache.  SDRAM has access time ranging from7–10 nanoseconds.
  25. 25.  Anatomy of Hybrid Disk. ◦ DRAM are nanosecond devices. ◦ NAND chips are microsecond devices. ◦ NAND flash memory can play as an intermediate layer (e.g., a nonvolatile cache) between the DRAM and traditional disk drives. ◦ Hybrid disk integrates NAND flash memory into a standard disk drive as a second level cache. ◦ Hybrid disk consists of three layers: disk cache, NANDflash memory, and magnetic platters. Solid State Disk ◦ SSD refers to semiconductor devices ◦ consists of either DRAM volatile memory or NAND flash nonvolatile memory. ◦ DRAM-based SSD requires an internal battery and backup disk drive. ◦ current SSDs employ nonvolatile flash memory as the storage media (e.g., USB memory sticks).
  26. 26.  The challenges (e.g., endurance cycles, erase before write, etc.) presented by NAND flash memory indicate that the flash memory could fail before the magnetic disk. Spinning up the magnetic platters takes extra time and power. This incurs noticeable delay and power penalty. Spinning down/up the magnetic platters too often also has a significant impact on reliability.
  27. 27.  Disk has to stay in the low-power state for a sufficiently long period of time which save the energy . This energy needed to spin the disk up again. This techniques is difficult to implement in SSDs because the energy required to start SSDs is more than a spanning up the server hard disk. Decreasing the RPM can significantly reduce the power consumption of disk drives. However, lower RPM can further worsen the performance of large-capacity disk drives.
  28. 28.  In the past 50 years, disk drive architecture has remained largely unchanged. They have reached a turning point at which they have to be reborn in order to further improve their performance and reduce power consumption while still maintaining high reliability. Hybrid disk is a temporary approach ◦ Therefore, an architecture shift is required to achieve this goal.
  29. 29. Thanks

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