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What is that boot time drive clicking noise?



Part of what causes this clicking problem is related to the power on routine functions. The boot sequence of a drive is as follows:
  • 1. Power on chip returns status
  • 2. Self check.
  • 3. Spindle spin up.
  • 4. Un-mounting heads from rack.
  • 5. Servo timing reads - firmware.
  • 6. SA reading - firmware.
  • 7. Firmware extensions reading.
  • 8. Error - read SA from other secondary copies.
The first thing a hard drive will do after it receives power is check for a return status from its chips to make sure the electronics are functioning. Then the drive will begin the self-check of its parts and wait for a return status. If both status checks are returned then the drive continues on to the next step and spin up the spindle.
The drive begins to spin the spindle the platters begin to revolve. When the platters begin to revolve the air flow around the platter creates a force that is called an air bearing. This air bearing will fling off debris on the platters such as any dust particles or metal fragments from the standard operation of the drive. This air bearing also causes the plastic locking arm mechanism to move out of the way as soon as there is enough air flow for the head to float. Without that airflow the arm is locked in place and will not move over the platter. This is a way to protect the platter from the head touching the platter and causing physical damage. The opposite is true during a power down. When power is cut to the drive, during the last revolutions of the motor, it generates enough power to move the head back to it park position. Because of this, if drive get enough power on and power off cycles in a row it is possible for the head to be stuck in the center of the platter and never to be parked correctly causing several types of damage. In certain drives it is common for the head to be stuck to the center of the platter, never having parked and keeping the platters from spinning. In most cases there is very little damage if the drive is opened and manually turned slow enough not to damage the head, and the data can be recovered, obviously never using this drive again.
If the all has proceeded correctly the air bearing will allow the head to float over the platter allowing it to move freely without scratching the surface of the platter. if the head is reading the Servo Timing info from the platter and relaying it to the circuitry so the controller knows the exact information for the placement of data.
After that head moves to the System Area (SA) of the platters and reads the content that it requires as well as any additional firmware and overlays. Most of the time, the system area is on the outer tracks - the extreme outer edge.
Learn more about hard drives System Area ..
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