Hard Disk Drives PDF CST8208

Hard Disk Drives CST8208 1 Hard Disk Drives  The hard disk drive is the main storage device for most modern computers.  The hard drive stores the data of a computer system including files, applications and operating systems.  Early hard drives were quite slow and...

Hard Disk Drives CST8208 1 Hard Disk Drives  The hard disk drive is the main storage device for most modern computers.  The hard drive stores the data of a computer system including files, applications and operating systems.  Early hard drives were quite slow and unstable, but they have evolved to be much faster and more reliable. 2 Hard Drive Advancements  Storage capacity Originally 5MB  Now up to 8TB+  Data transfer rates Originally 85KBps  Now 150MBps+  Access time Originally around 85ms Now 10-20ms  Cost $2,000 for 10MB  Now well under $100 for 1TB 3 Inside a Hard Drive 4  Inside a Hard Drive  Some major internal components of a hard drive Platters Read/write heads Actuator arms Spindle Motors Air Filters 5 Inside a Hard Drive  Platters Hard drives use rugged and solid platters to store data Platters are made from aluminum or a ceramic composite material They are quite light and have very low thermal expansion 6 Inside a Hard Drive –Air Filters  Most hard drives have two air filters Recirculating filter  Filters the small particles scraped off the platters Barometric filter  Provides venting to enable pressure equalization 7 Care of your hard disk drive  Do not expose your hard disk drive to extreme temperatures For example the trunk of your car during cold winter days or hot summer days If it must be exposed to extreme temperatures, wait until it has reached safe operational temperature before powering it on 8 Inside a Hard Drive  Read/write heads Both sides of each platter are coated to provide separate magnetic surfaces for data storage Every platter requires two read/write heads, one for each side The heads do not make contact with the platter during use, they float on a very thin cushion of air The air buffer is extremely small (see the following illustration for just how small) 9 Read/Write Head 10 Inside a Hard Drive  Actuator Arm The read/write heads are located on the tip of the actuator arm In modern hard drives, the actuator arm is moved by the voice coil motor  Spindle Most hard drives have several platters separated by spacers and clamped to a rotating spindle The spindle, and the platters, are rotated at a constant speed 11 Inside a Hard Drive  Voice coil motor All hard drives today use a linear motor, or voice coil to move the heads and actuator arms When electrical current is applied a magnetic field is generated that moves the actuator arm Much faster, accurate and more reliable than the previous type (stepper motor) Hard drive heads are automatically parked 12 Full Speed Ahead  Most hard drives today spin at a rate of either 5,400 rpm or 7,200 rpm  Some high performance drives spin at a rate of 10,000 rpm  Very high performance drives spin at rates up to 15,000 rpm 13 Hard Drive Assembly  Hard drives are assembled in sealed clean rooms under sanitary conditions  A tiny spec of dust can cause a hard drive head to crash  Few companies have the facilities to manufacture or repair hard drives Repair is expensive Malfunctioning drives are usually just replaced 14 Hard Drive Organization  The hard drive can be divided into the following areas: Tracks Cylinders Sectors Clusters 15 Hard Drive Organization  Tracks Each platter consists of multiple concentric circles called tracks A typical platter contains thousands of tracks Tracks 16 Hard Drive Organization  Cylinders Defn: A group of tracks of the same diameter is called a cylinder Each track is located directly over the same track on subsequent platters The number of tracks on one side of a platter is therefore equal to the number of cylinders in a hard drive 17 Hard Drive Organization  Sector A sector is a section of a track A sector is the smallest unit of space on your hard drive that can be allocated Traditionally held 512 bytes of data Some newer “Advanced Format” drives hold 4 KB per sector  (3 sectors highlighted) 18 Hard Drive Organization  Cluster A cluster is a number of sectors ranging from 2 to 64 depending on how the drive is formatted A cluster is the smallest amount of space that can be used for any read/write operation 19 Terms to Know  Seek time is the time that it takes for a disk arm to move into position over the desired cylinder.  Rotational delay is the time that it takes for the desired sector to move into position beneath the read-write head.  access time = Seek time + Rotational delay  Transfer rate is the speed at which data is transferred from the drive to the system after it has been accessed 20 Hard Drive Setup  The following values represent the hard drive geometry in the BIOS/CMOS setup: Cylinders Heads Sectors per track  The BIOS needs to know the hard drive geometry in order to access it properly  Modern computers can query the drive to determine these values 21 Obsolete geometry  Write precompensation cylinder Sectors on the inside of the drive are smaller than the sectors on the outside Drives would increase sensitivity of the heads to read the smaller sectors. The cylinder at which this began was called the write precompensation cylinder  Landing Zone A landing zone was an unused cylinder where the heads could be parked 22 Logical Block Addressing (LBA)  Modern hard drives use LBA as the method of addressing sectors  Each sector is assigned a unique identifier, or sector number  The BIOS in older computers used 28-bit addressing, which limited hard drives to 137 GB  Current systems support 48-bit addressing, pushing the limit to 144PB 23 Hard Drive Interfaces  Three major hard drives interfaces exist SATA  Serial ATA – 7 pin data connector PATA  Parallel ATA – 40 pin data connector SCSI  Small Computer System Interface – variety of connectors, typically used in servers 24 Capacity Confusion  Some manufacturers of hard disk drives calculate the capacity in GB by dividing by 1000.  This results in advertising a significantly higher number than the formatted drive capacity that’s reported by the operating system. 25 Head Crash  A head crash is a hard-disk failure that occurs when a read–write head of a hard disk drive comes in contact with its rotating platter, resulting in permanent damage to the magnetic media on the platter surface (the circular mark in the picture.) A head crash can be initiated by dirt, or excessive shock or vibration. 26 Head Crash 27 SMART – Self-Monitoring Analysis and Reporting Technology  SMART provides an interface for monitoring various aspects of hard drive performance and condition.  Most hardware failures are predictable. SMART provides vital information that can allow the advance notice necessary to backup data and have a replacement drive made available in the case of imminent failure 28 SMART  SMART can provide information on a large number of hard drive aspects including: Internal temperature Power on hours Spin up retry count Power cycle count Seek error count Throughput performance …and many more 29 SMART  While most hard drives support SMART, most people do not monitor it.  Software is required to collect and display the SMART data. There are freeware/shareware software solutions as well as relatively inexpensive SMART interface programs that can be purchased. 30