17.SecondaryStorage

17.SecondaryStorage - IntroductiontoI/Oand DiskManagement 1...

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1 Introduction to I/O and  Disk Management
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2 Secondary Storage Management Disks — just like memory, only different Why have disks? Memory is small. Disks are large. Short term storage for memory contents (e.g., swap space). Reduce what must be kept in memory (e.g., code pages). Memory is volatile. Disks are forever (?!) File storage. GB/dollar dollar/GB RAM 0.013(0.015,0.01) $77($68,$95) Disks 3.3(1.4,1.1) 30¢ (71¢,90 ¢ ) Capacity : 2GB vs. 1TB 2GB vs. 400GB 1GB vs 320GB
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3 How to approach persistent storage Disks first, then file systems. Bottom up. Focus on device characteristics which dominate performance or reliability (they become focus of SW). Disk capacity (along with processor performance) are the crown jewels of computer engineering. File systems have won, but at what cost victory? Ipod, iPhone, TivO, PDAs, laptops, desktops all have file systems. Google is made possible by a file system. File systems rock because they are: Persistent. Heirarchical (non-cyclical (mostly)). Rich in metadata (remember cassette tapes?) Indexible (hmmm, a weak point?) The price is complexity of implementation.
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4 Different types of disks Advanced Technology Attachment (ATA) Standard interface for connecting storage devices (e.g., hard drives and CD-ROM drives) Referred to as IDE (Integrated Drive Electronics), ATAPI, and UDMA. ATA standards only allow cable lengths in the range of 18 to 36 inches. CHEAP. Small Computer System Interface (SCSI) Requires controller on computer and on disk. Controller commands are sophisticated, allow reordering. USB or Firewire connections to ATA disc These are new bus technologies, not new control. Microdrive – impressively small motors
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5 Different types of disks Bandwidth ratings. These are unachievable. 50 MB/s is max off platters. Peak rate refers to transfer from disc device’s memory cache. SATA II (serial ATA) 3 Gb/s (still only 50 MB/s off platter, so why do we care?) Cables are smaller and can be longer than pATA. SCSI 320 MB/s Enables multiple drives on same bus Mode Speed UDMA0 16.7 MB/s UDMA1 25.0 MB/s UDMA2 33.3 MB/s UDMA3 44.4 MB/s UDMA4 66.7 MB/s UDMA5 100.0 MB/s UDMA6 133 MB/s
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6 Flash: An upcoming technology Flash memory gaining popularity One laptop per child has 1GB flash (no disk) Vista supports Flash as accelerator Future is hybrid flash/disk or just flash? Erased a block at a time (100,000 write-erase-cycles) Pages are 512 bytes or 2,048 bytes Read 18MB/s, write 15MB/s Lower power than (spinning) disk GB/dollar dollar/GB RAM 0.013(0.015,0.01) $77($68,$95) Disks 3.3 (1.4,1.1) 30¢ (71¢,90 ¢ ) Flash 0.1 $10
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7 Anatomy of a Disk Basic components 0 1 2 s –1 . Block/Sector Track Cylinder Platter Surface Head Spindle
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8 Disk structure: the big picture Physical structure of disks
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9 Anatomy of a Disk Seagate 73.4 GB Fibre Channel Ultra 160 SCSI disk Specs: 12 Platters 24 Heads Variable # of sectors/track 10,000 RPM Average latency: 2.99 ms Seek times Track-to-track: 0.6/0.9 ms Average: 5.6/6.2 ms Includes acceleration and settle time.
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This document was uploaded on 03/09/2012.

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17.SecondaryStorage - IntroductiontoI/Oand DiskManagement 1...

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