An Introduction to Hard-Disk Drives Adopted from Seagate Tutorial at FAST’07
Agenda • Background • New Technologies • Research Works • Useful Links
Background The first hard drive of IBM’s RAMAC in 1956
Background 5MB Hard Disk in 1956
Background A typical SCSI hard drive
Background Read/Write Head Movement
Background Close-up of a hard disk head
Background Hard drive Internals
Background A hard disk surface with 3 zones
Background On-board disk drive logic
Background Disk drive module
Background Higher BPI & TPI, Higher capacity
Background Areal Density vs. Moore’s Law
Background Seagate Products in 2006
Background Response time = Seek Time + Rotation Latency + Xfer Time
Background • First-in, first-out (FIFO)
Background • Shortest Service Time First
Background • SCAN
Background • C-SCAN
Standard 512 byte Format Servo Data 1 Data 2 Data 3 Servo Data 4 Non-Standard Format (allows for post amble check field) Servo Data 1 Data 2 Data 3 Data 3 Servo Data 4 Background • Industry has standardized on 512 byte sectors • H/w and s/w optimized for efficiency, cost and µP loading • Manufacturing geared up for “vanilla” processes and production • Problems with changing the sector size: • More buffering required to handle the additional data • More complex f/w requiring additional memory storage • More complex split sector handling/computation required • More complicated/costly media flaw mapping process
New Techniques • IntelliSeek (Western Digital) • GreenPower (Western Digital) • Hybrid Disk (Samsung & Seagate) • Background Media Scan(BMS) (Seagate) • Idle Read After Write(IRAW) (Seagate)
IntelliSeek • Ideas • WD's IntelliSeek technology proactively calculates an optimum seek speed to eliminate hasty movement of the actuator that produces noise and requires power • With IntelliSeek, the actuator's movement is controlled so the head reaches the next target sector just in time to read the next piece of information, rather than rapidly accelerating and waiting for the drive rotation to catch up.
IntelliSeek • http://www.wdc.com/en/flash/index.asp?family=intelliseek
GreenPower • IntelliPower™ • A fine-tuned balance of spin speed, transfer rate, and caching algorithms designed to deliver both significant power savings and solid performance. For each drive model, WD may use a different, invariable RPM. • IntelliPark™ • Delivers lower power consumption by automatically unloading recording heads during idle to reduce aerodynamic drag, and disengages read/write channel electronics.
Hybrid Disk • First, Hybrid HDD has flash memory playing a supplementary role to DRAM in order to dramatically reduce the boot time and improve system capacity. • Secondly, Hybrid HDD enables write-caching of regular data using flash memory in order to minimize the need for the hard disk drive to spin-up. • Thirdly, Hybrid HDD offers improved durability and reliability. Insofar as the need for the HDD to spin-up is minimized, this also serves to shorten the duty cycle of the HDD, lowering the probability of head-media collisions and errors (off-track write, etc). This can lead to increasing the MTBF.
BMS & IRAW • The second generation of Seagate-exclusive Background Media Scan (BMS) proactively scans the media for potential defects during drive idle time. It enables incipient errors to be corrected before data is lost. • Seagate-exclusive IRAW (Idle Read After Write) enhances data protection by verifying—during drive idle time—that data in the drive buffer was properly written.
Research Projects • Multi-Zones • FreeBlock Scheduling • Track-Aligned Extent • Multimap
Multi-Zones • PROFS (MASCOT ‘01) • Performance-Oriented Data Reorganization for Log-structured File System on Multi-Zone Disks • Ideas • reorganizes data on the disk during LFS garbage collection and system idle periods • puts active data in the faster zones and inactive data in the slower zones
Freeblock Scheduling • SIGMOD ‘00, OSDI ‘00, FAST ‘02, FAST ’04 • Ideas • a new approach to utilizing more of a disk's potential media bandwidth by filling rotational latency periods with useful media transfers • By interleaving low priority disk activity with the normal workload, one can replace many foreground rotational latency delays with useful background media transfers.