Dennis Yi Harada CS162 Spring 05 03/16/05 Last Class before spring break Professor passed in 3 toys for us to check them out. A cd drive, and 2 Disk drive Lecture was based on advanced in Technology in system design, Disk, Storage, and Optical Storage. This lecture was bassically based on graphs which we can read on the reader. As professor shows a graph I will try to reference the page in the reader where you can access it. - A disk is a "hard, flat version of a tape": they have a write head which magnetizes little spots on the disk surface, but disks use synthetic metals in place of iron - Most disks are fixed-sector devices, with blocks of data and interrecord gaps, error correction bits, etc. System Design In developing new technology factors like sound (noise), size, reliability, speed, cost are important in the fabrication of new products. If you have your laptop on in a big room, it's ok, but if you are at your house by yourself, you probably feel like it makes a lot of noise. Here professor shows a table ( "Table-1 1.8" HDD, Major specifications) We don't need to memorize it completely, but at least a factor of 3-4 Professor shows another graph page 136 in the reader. Talks about Areal Density vs calendar year. It uses calendar year because in Japan they use Rain system. Most of the companies that produces devices are japanese, so it's important to mention this. Next graph is figure 3 in reader (pag. 137) Shows performance history of IBM disk products with respect to data rate Rapid increase usually means change in technology Next graph is figure 6 in reader (pag. 139) Shows Head-to-media spacing in IBM magnetic hard direves vs. product areal density Spacing between head and disk becomes small enough that air bearings and lubrication deviate substantially from their present behaviour, and where surface roughness cannot be scaled smaller because it's approaching atomic dimensions 3 important things about spacing are: the height of the disk, the size of the magnetic particles and the width of the gap in the read head must improve the 3 at the same time to improve disk, not much change if only improves one Then professor talks about reliability. Before disks cost around $30,000 and they didn't break much Now disks cost < than $100, where they tell us that they have 1 million/hour to faliure # of zeros meantime to faliure doesn't mean anything, is better to have 2 disks Producers are not looking for the best disk, but the cheapest one. They don't care if the loos on every one, but they win in volume saled. There is an agopolly which is when the consumer sets the price. Oppossite from monopolly Data on Disk is better than data on Tapes. Product lifetime in Disk is about 3 months. After that they are replaced by something newer and denser Will 1 inch today become 1 cm tomorrow? Next graph is figure7 in reader (page. 156) Shows Cost of storage for disk drive, paper film and semiconductor memory. Professor talks about sharp down curves. Significant price decrease in semiconductor memory storage has also influenced the system price trend to a certain extend, as can be seen in the declining price-per-storage-capacity trend Next graph is figure1 in reader (pag. 234) Refers to same thing as previous graph, with the difference that it talks about decrease of HashCurve, MicroDrive and HDD's Next graph is figure2 in reader (pag. 136) Shows Price history of hard disk producst vs. year of product introduction As we can see, the price of a megabyte has decrease very rapidly from more than $100 in 1980 to $0.1 in 2000 Next graph is reader pag. 215, Capacity Trend by Form Factor slide This graph is from Toshiba, not really updated, but don't look at actual numbers, but at the curve that shows that eventhough things are smaller, they can store more capacity Next graph is reader pag. 214, Form Factor, Media size Shows different Disks sizes, where they stress the fact the as the Disk size decreases, the data zone decreases, and the radius too Next graph is reader page 214, Form Factor, Comparison of Foot print Shows the physical size of a disk as a rectangular area. Next graph is figure4 in reader (pag. 137) Performance history of IBM disk products with respect to access time Curve isn't that steep, cpu doubling every 2 years, disk doubling every 7 years Next graph is figure 3 in reader (pag. 137) Performance history of IBM disk products with respect to data rate We analyze the rate at which bits go from magnetic surface to disk head Question: Why doesn't diks spin really fast? 3 reasons: a) Before disk was 360 rpm, at 60 hertz, but the DC motor can go at any speed you want cause it can blow up. b) Smaller radius causes a faster spin making the signal of the read head not accurate. square waves become sinusodal waves because it's too fast to read c) There is too much air creating turbulance. Need more power to push the air creating noise Question: Is heat an problem? Yeah heat is a problem, eventhough heat is power Next graph is figure2 in reader (pag. 154) Storage floor space utilization trend Here we see the Raw capacity per floor space area Joke: exam question: How many disks can we store in this room? ex. Google has to worry about power consumption at a server farm) Next graph is figure3 in reader (pag. 155) Floor space required to store 1 terabyte Floor spaced required to store on terabyte of information over the past 45 years is shown to have decreased by more than a factor of e^7, similar to increases in server disk drive areal density Next graph is figure4 in reader (pag. 155) Hard disk drive volumetric density trend This value is doubling every year. Number of GB per cubic inch in real-life terms Next graph is figure1 in reader (pag. 154) Hard diks drive areal density trend Shows Areal density Megabyte/sp. inch Shows cumulative annual growth rate, magneto-resistive heads, giant magneto-resistive, anti freomagnetically coupled Everytime there's a change in technology, there's improvement Next graph is figure7 in reader (pag. 156) Cost of storage for disk drive, paper, film, and semiconductor memory This graph shows the Price per megabyte. Not a very steep curve Next graph is figure6 in reader (pag. 156) Cost of storage at disk drive and system level This graph compares disk drive, paper & film, and semiconductor storage costs Much cheaper to store on disk than in a real notebook Obviously, paper/film storage depends on font size/resolution, but there is a limit (the precise number is not critical) Next graph is figure8 in reader (pag. 157) The evolution of disk drive form factors Big change from a 24 inch with a form factor of 5mb, to a a inch with form factor of 1gb Next graph is figure9 in reader (pag. 158) Hard disk drive and storage system power trend per Gbytes stored Kilovolt amps (watts) per GB Cheaper to store bytes than paper notes Left curve is for storage systems and right curve is for hard disk drives Next graph is figure10 in reader (pag. 158) Hard disk drive maximun internal data rate for entreprise/server drives Inside to outside of disk Before same number fo bits in all tracks. Very convinient for OS. Constant data arrray. Very simple arithmetic. Lay out everything on disk. Optimize I/O Problem is that is not very efficient. Bits too fast to store, can't read properly so solution is different # of bits per track. 6 to 8 zones, different bit capacities. Hard to increase number of zones. Before disk controlers not very smart out of 4 models. OS knew everything. Now, there are a lot of different models that change every 3 months. All intelegence is in physical disk drive. Only block number and disk go and tranlated to physical address. There's a limited number of accepted data arrays that cause tracks not to change. Timing track and used a clock now all self clocking. More bits in outer track. Next graph is figure11 in reader (pag. 159) Disk drive access/seek times Seek time = (actuator inertialpower)^1/3 x (data band)^2/3 Rotational time (latency) = (rpm)^-1 Access time = seek time + latency Next graph is figure12 in reader (pag. 159) Performance trend for hard disk drives and storage systems Change in technology: Addition of system cache and addition of HDD buffer Next graph is figure2 in reader (pag. 220) Acoustic Noise (Sound Power) Example of a laptop, in big room doesn't bother, in quiet room could be noisy. The bigger the disk the noisy it is Next graph is figure2 in reader (pag. 224) Microdrives: Selected Specs This graph shows us the diferent Specification of a Gen 1 (340 MB) and a Gen 2 (1.0 GB) This is kind of old, but again look at trends not actual numbers. These are microdrives, drives that you can stick into your digital camera example of ipod: You can throw them and they won't break, but they still have a limit if you throw them from the second floor, they'll probably break. Next graph is about External Storage: Summary of features, couln't find in reader, but refers to a list of price versus capacity. Now prices are really low. Next graph is about Historical rates of increase in linear, track and areal density linear is 21% Track is 24% Density is 49% Next graph is about Actual seek and rotational time as percentage of manufactor specified values. Couln't find graph in reader but it refers to percentage of actual seek/rotational time as a function of the manufacturer's specified values Data placement isn't random. There's no random place on disk Disk I/O Seek, move the head to right track Set sector. In the old days OS did this, now disk does it. Do the read/write RPS miss, interrupt for disk when is not ready to read, so it uses the read buffer Disk Characteristics Sizes of disks available: 5.25" (dissapearing), 3.5" (desktop), 2.5" (laptop), 1.8" (ultra portable), 1" (compact flash), 2.5" drives available up to ~80GB 3.5" Sector sizes still 512 bytes, goes back 30 years Areal density higher now, but still 30-60GB/sq. inch 15k RPM drives are server drives, which are powerful and loud Laptop drives are smaller and quieter Seek time 3-5ms Maximum seek time is from disk edge to disk edge Media transfer rate up to 650Mbit/sec (off disk surface) Can sustain up to ~98MB/sec (from buffer) Bit error rates: 1/10**12 (recoverable, with error correction), 1/10**16 Reliability: >= 300k hours MTBF (Prof: "I don't think so."), min. 50k stop/start cycles Startup time: 1-10 sec Maxtor Atlas 15K II, example specific disk, in reader (pag. 251) 147 GB, 4 platters, 8 heads 512 byte sectors Interface Ultra 320 SCSI Average seek 3-3.8 ms Max seek 9ms Track to track seek .3-.5ms 15,000 rpm sustained data rate 98MB/sec 8MB cache Altitude max 36db noise Characteristics of Modern Disks They are smaller, usually 3.5" 2.5" and 1.8" for laptops, PC cards 1.0" for cameras They are all map by the controller 35% more capacity with same number of bits per track Solid State disk (SSD) Faster disk, semiconductor that looks like a disk, so no new interface cause looks like old disk Antique Technology Drums | | _______ | |-- | |---- heads | |----- | |----- | |------ | | |_______| | | Late 60's mid 70's 1st generation drums were extremely expensive "Data Cell" invented by IBM, nobody else thought could be made. Only lasted 1 generation since it was too expensive, and didn't quite work. The idea was to have a strip of tapes. Cheap disk per byte. Tape is cheap. Optical Disk (CD) Compact Disk Constant angular velocity Seek time is slow, 35ms Latency is very slow as well as Transfer rate Technology hasn't change in 10 years Constant linear velocity, speed changes but bit density is constant Magneto-optic Laser heats up surface with an external magnetic field that polarizes it, and a weak laser reads it 1X CD-ROM has a transfer rate of 150KB/sec The fastest you can spin a CD is about 12x (a higher speed rating refers to data being read from outer tracks) Like clasical music that goes faster and faster, and faster Modern CD Drives Constant angular velocity, so data rate varies Maximum data rate only at outside of diskS Still only read at a certain rate Better rate if multiple tracks are read at once Manufactured discs have pressed, physical pits DVD Capacity 4.5GB, 9GB, 18 GB two-sided two layered Use red light, unlike infrared of CDs, so resolution improves, bits get smaller, and you can fit more bits on a disc Next graph is figure in reader (pag. 282) DVD Burners Whole bunch of different layers: protective, dielectric, recording, dielectric, reflective, protective, label Next graph is figure in reader (pag. 276) Storing more data Detailed view of cd layers Next graph is figure in reader (pag. 278) Layer1, Reflective coating, organic dye Layer0, semireflective coating, organic dye Light can leak through to layer1 even when the laser is focused on layer0 When layer1 is being recorded, some light is lost in reflections off layer0 Pick up your exams if you haven't yet You don't have to remember all the graphs for the midterms, but try to understand them and see general trends. Don't need to remember all the exact values of charts but at least a good idea.