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Seagate ships billionth drive!

Computer Structures and Design Lecture 30 – Disks 2008-04-28. Lecturer SOE Dan Garcia. How much storage do YOU have?. The ST506 was their first drive in 1979 (shown here), weighed 5 lbs, cost $1,500 and held 5 MeB. Today’s drives hold 1 TB, and are available for less than $200.

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Seagate ships billionth drive!

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  1. Computer Structures and DesignLecture 30 – Disks2008-04-28 Lecturer SOE Dan Garcia How much storage do YOU have? The ST506 was their first drive in 1979 (shown here), weighed 5 lbs, cost $1,500 and held 5 MeB. Today’s drives hold 1 TB, and are available for less than $200. Seagate ships billionth drive! 1b.seagatestorage.com

  2. Magnetic Disk – common I/O device Computer Keyboard, Mouse Devices Processor (active) Memory (passive) (where programs, data live when running) Input Disk, Network Control (“brain”) Output Datapath (“brawn”) Display, Printer

  3. Magnetic Disk – common I/O device • 一种计算机存储器 • 信息存储在旋转盘的磁性材料的表面 • 和录音机类似，但这里记录的是数字量而非模拟量 • 非易失性存储（Nonvolatile storage） • 掉电时数据依然存在. • 两种类型 • 软盘 – slower, less dense, removable. • 硬盘 (HDD) – faster, more dense, non-removable. • 在计算机系统中的作用 (硬盘驱动器): • 用于长期, 廉价地存储文件 • 主存的备份“Backup”. 大容量, 低价格, 在存储结构中处于较底的层次 (虚拟内存)

  4. { Platters (1-12) Photo of Disk Head, Arm, Actuator 轴Spindle Arm Head Actuator

  5. Sector Disk Device Terminology • 多个盘片, 信息以磁的方式记录在盘的两个表面(usually) • Bits记录在道上, 可进一步分为扇区(e.g., 512 Bytes) • Actuator moves head(end of arm) over track (“seek”), wait for sectorrotate under head, then read or write Inner Track Outer Track Arm Head Platter Actuator

  6. Disk Device Performance (1/2) • 磁盘反应时间 = Seek Time + Rotation Time + Transfer Time + Controller Overhead • Seek Time? 依赖于arm要移动几条道, actuator的速度 • Rotation Time? 依赖于磁盘旋转的速度, 扇区离头的距离 • Transfer Time? 依赖于磁盘的数据率 (带宽) (f(bitdensity,rpm)), 及所访问的数据大小 Inner Track Sector Outer Track Head Controller Arm Spindle Platter Actuator

  7. Disk Device Performance (2/2) • 头移动到扇区的平均距离? • 转一圈的一半时间 • 7200转/分 120 转/秒 • 1 转 = 1/120 秒 8.33 毫秒 • 1/2 转 (revolution)  4.17 ms • arm移动的平均道数? • 磁盘工业标准测试: • 对各种可能的道求出所有寻道距离，加起来/ 所有可能个数 • 假定平均寻道距离是随机的 • 磁盘cache的大小会极大影响性能! • Cache内建于磁盘系统, OS不知细节

  8. Data Rate: Inner vs. Outer Tracks • 为了简化, 最初每道具有相同个数的扇区 • 由于外道更长, 每寸的位数更少 • 由于竞争的需要对所有的道都保持较高的每寸位数 (BPI) (“位密度为常数”) •  每个磁盘更大容量 •  边缘处每道有更多的扇区 •  由于磁盘以常速旋转,外道有更快的数据率 • 外道带宽是内道的1.7倍!

  9. Disk Performance Model /Trends • 容量 : + 100% / year (2X / 1.0 yrs) • 随着时间的发展, 增长速度如此之快以至于盘片数减少了 (现在有些只用1片!) • 传输率 (带宽) : + 40%/yr (2X / 2 yrs) • 转速+寻道时间 : – 8%/yr (1/2 in 10 yrs) • 面密度 • 沿道记录的位数: Bits/Inch(BPI) • 每面的道数: Tracks/Inch(TPI) • 我们关心单位面积的位密度Bits/Inch2 • 称为面密度=BPI x TPI • “~120 Gb/In2 is longitudinal limit” • “230 Gb/In2 now with perpendicular” • GB/$: > 100%/year (2X / 1.0 yrs) • Fewer chips + areal density

  10. 性能 企业应用, 服务器 E.g., Seagate Cheetah 15K.6 3 Gb/s,Serial Attached SCSI,Fibre Channel 450 GB, 3.5-inch disk 4 disks, 8 heads 15,000 RPM 12-17 watts (idle-normal) 3.4 ms avg. seek 164 MB/s transfer rate 1.6 Million Hrs MTBF 5 year warrantee $1000 = $3.30 / GB 容量 主流, 家庭使用 E.g., Seagate Barracuda 7200.11 SATA 3Gb/s NCQ,SATA 1.5Gb/s NCQ 1 TB, 3.5-inch disk 4 disks, 8 heads 7,200 RPM 8-12 watts (idle-normal) ?? ms avg. seek (上次8.5) 115 MB/s transfer rate 0.75 Million Hrs MTBF 5 year warrantee $200 = $0.20 / GB State of the Art:Two camps (2008) These use Perpendicular Magnetic Recording (PMR)!! source: www.seagate.com

  11. 1 inch disk drive! • Hitachi 2007 release • 由iPods& 数码相机驱动 • 8GB, 5-10MB/s (higher?) • 42.8 x 36.4 x 5 mm • 垂直磁记录 (PMR) • FUNDAMENTAL new technique • Evolution from Longitudinal • Starting to hit physical limit due to superparamagnetism（超顺磁性） • They say 10x improvement www.hitachi.com/New/cnews/050405.html www.hitachigst.com/hdd/research/recording_head/pr/

  12. Where does Flash memory come in? • Microdrives and Flash memory (e.g., CompactFlash) are going head-to-head • 都不易失 (no power, data ok) • Flash优点: 更耐用 & 低功耗(无移动部件, 微硬盘需要上下旋转) • Flash限制: 写的次数有限 (围绕电荷存储装置的绝缘氧化层的磨损) • How does Flash memory work? • NMOS晶体管，在门和源/出口间有附加的导体来 and “捕获traps”电子. 有/无电子对应于1或0. en.wikipedia.org/wiki/Flash_memory

  13. en.wikipedia.org/wiki/Ipodwww.apple.com/ipod What does Apple put in its iPods? Toshiba flash1, 2GB Samsung flash4, 8GB Toshiba flash 8, 16, 32GB Toshiba 1.8-inch HDD80, 160GB shuffle, nano, classic, touch

  14. Use Arrays of Small Disks… • Katz and Patterson asked in 1987: • 可否使用更小的磁盘来缩小磁盘和CPU性能间的鸿沟? 传统: 4磁盘设计 3.5” 5.25” 10” 14” High End Low End 磁盘阵列: 1磁盘设计 3.5”

  15. Replace Small # of Large Disks with Large # of Small! (1988 Disks) IBM 3390K 20 GBytes 97 cu. ft. 3 KW 15 MB/s 600 I/Os/s 250 KHrs $250K x70 23 GBytes 11 cu. ft. 1 KW 120 MB/s 3900 I/Os/s ??? Hrs $150K IBM 3.5" 0061 320 MBytes 0.1 cu. ft. 11 W 1.5 MB/s 55 I/Os/s 50 KHrs $2K 容量 体积 功耗 数据率 I/O Rate MTTF Cost 9X 3X 8X 6X 磁盘阵列具有更高的性能, 每单位体积更高的容量, 单位功耗更高的容量, 可靠性?

  16. Array Reliability • 可靠性 – 是否有一个组件失效 • 测量方法：平均故障时间 (MTTF) • N个磁盘的可靠性= 单个磁盘的可靠性 ÷ N(假定故障是独立的) • 50,000 Hours ÷ 70 disks = 700 hour • 磁盘系统平均故障时间: 从6年降为1个月! • Disk arrays too unreliable to be useful!

  17. Redundant Arrays of (Inexpensive) Disks • 文件 “条状”分布于多个磁盘 • 冗余产生高数据可用性 • 可用性: 即使一些组件出现故障，仍能为用户提供服务 • 磁盘仍会出故障 • 内容通过存储在阵列中的冗余数据重建  由于存储冗余信息，容量减少  由于更新冗余信息，带宽减少

  18. Berkeley History, RAID-I • RAID-I (1989) • 由以下部件组成：带有128 MB内存的Sun 4/280工作站, 四个双路（dual-string） SCSI控制器, 28 5寸SCSI 磁盘及专用的磁盘条带化软件 • Today RAID is > tens billion dollar industry, 80% nonPC disks sold in RAIDs

  19. “RAID 0”: No redundancy = “AID” • 本例中有四个磁盘, 块组织方式 • 更快的访问速度，因为可同时从多个磁盘传输数据 This and next 5 slides from RAID.edu, http://www.acnc.com/04_01_00.htmlhttp://www.raid.com/04_00.htmlalso has a great tutorial

  20. RAID 1: Mirror data • 每个磁盘完全复制到其 “镜像” • 可以获得极高的可用性 • 写数据带宽减少: • 1 逻辑写 = 2 物理写 • 非常昂贵的解决方案: 100% 容量浪费

  21. RAID 3: Parity • 计算出各组的奇偶效验存储到P磁盘，以此来保护磁盘减少故障 • 逻辑上, 单个高容量, 高传输率磁盘 • 本例中，奇偶效验会多出25%容量，而 RAID 1 多出１００％，(5 disks vs. 8 disks)

  22. Inspiration for RAID 5 (RAID 4 block-striping) • Small writes (write to one disk): • 方案1: 读其他磁盘的数据, 产生新的和，然后写奇偶效验盘(访问所有磁盘) • 方案2: 由于P拥有旧的和,比较新、旧数据, 差值加到P: 1 逻辑写 = 2 物理读 + 2 物理写到两个磁盘 • 奇偶效验盘是Small writes的瓶颈: 例如要写A0, B1都要写P盘 A0 B0 C0 D0 P D1 P A1 B1 C1

  23. RAID 5: Rotated Parity, faster small writes • 由于校验盘交错，分别写成为可能 • 例如: 写A0, B1会用到 0, 1, 4, 5磁盘, 因此可以并行处理 • 仍然是1 small write = 4次物理磁盘访问 en.wikipedia.org/wiki/Redundant_array_of_independent_disks

  24. Peer Instruction • RAID 1 (mirror) and 5 (rotated parity) help with performance and availability • RAID 1 has higher cost than RAID 5 • Small writes on RAID 5 are slower than on RAID 1 ABC 0: FFF 1: FFT 2: FTF 3: FTT 4: TFF 5: TFT 6: TTF 7: TTT

  25. “And In conclusion…” • 磁盘仍然高速增长: 容量60%/yr, 带宽40%/yr, 寻道时间更短, 旋转加快, MB/$每年增长100%? • Designs to fit high volume form factor • PMR a fundamental new technology • breaks through barrier • RAID • Higher performance with more disk arms per $ • Adds option for small # of extra disks • Can nest RAID levels • Today RAID is > tens-billion dollar industry, 80% nonPC disks sold in RAIDs, started at Cal

  26. Bonus slides • These are extra slides that used to be included in lecture notes, but have been moved to this, the “bonus” area to serve as a supplement. • The slides will appear in the order they would have in the normal presentation Bonus

  27. BONUS : Hard Drives are Sealed. Why? • The closer the head to the disk, the smaller the “spot size” and thus the denser the recording. • Measured in Gbit/in2. ~60 is state of the art. • Disks are sealed to keep the dust out. • Heads are designed to “fly” at around 5-20nm above the surface of the disk. • 99.999% of the head/arm weight is supported by the air bearing force (air cushion) developed between the disk and the head.

  28. Historical Perspective • 容量和尺寸，对于市场的影响要比对性能的影响大 • 尺寸因素的变革: 1970s: 主机系统  14 寸直径盘 1980s: 小型机, 服务器  8”, 5.25” diameter disks Late 1980s/Early 1990s: • PCs  3.5 inch diameter disks • Laptops, notebooks  2.5 inch disks • Palmtops didn’t use disks, so 1.8 inch diameter disks didn’t make it • Early 2000s: • MP3 players  1 inch disks

  29. Early Disk History (IBM) Data density Mbit/sq. in. Capacity of unit shown Megabytes 1973: 1. 7 Mbit/sq. in 140 MBytes 1979: 7. 7 Mbit/sq. in 2,300 MBytes source: New York Times, 2/23/98, page C3, “Makers of disk drives crowd even more data into even smaller spaces”

  30. Early Disk History 1989: 63 Mbit/sq. in 60,000 MBytes 1997: 1450 Mbit/sq. in 1600 MBytes 1997: 3090 Mbit/sq. in 8100 MBytes source: New York Times, 2/23/98, page C3, “Makers of disk drives crowd even more data into even smaller spaces”

  31. Disk Performance Example • Calculate time to read 1 sector (512B) for Deskstar using advertised performance; sector is on outer track Disk latency = average seek time + average rotational delay + transfer time + controller overhead = 8.5 ms + 0.5 * 1/(7200 RPM) + 0.5 KB / (100 MB/s) + 0.1 ms = 8.5 ms + 0.5 /(7200 RPM/(60000ms/M)) + 0.5 KB / (100 KB/ms) + 0.1 ms = 8.5 + 4.17 + 0.005 + 0.1 ms = 12.77 ms • How many CPU clock cycles is this?

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