Hard Disk Temperature Acclimation
Because hard disks have a filtered port to bleed air into or out of the HDA, moisture can enter the drive, and after some period of time, it must be assumed that the humidity inside any hard disk is similar to that outside the drive. Humidity can become a serious problem if it is allowed to condenseand especially if you power up the drive while this condensation is present. Most hard disk manufacturers have specified procedures for acclimating a hard disk to a new environment with different temperature and humidity ranges, and especially for bringing a drive into a warmer environment in which condensation can form. This situation should be of special concern to users of laptop or portable systems. If you leave a portable system in an automobile trunk during the winter, for example, it could be catastrophic to bring the machine inside and power it up without allowing it to acclimate to the temperature indoors.
The following text and Table below are taken from the factory packaging that Control Data Corporation (later Imprimis and eventually Seagate) used to ship with its hard disks:
Table; Hard Disk Drive Environmental Acclimation Table |
|
| Previous Climate Temperature | Acclimation Time |
| +40°F (+4°C) | 13 hours |
| +30°F (1°C) | 15 hours |
| +20°F (7°C) | 16 hours |
| +10°F (12°C) | 17 hours |
| 0°F (18°C) | 18 hours |
| 10°F (23°C) | 20 hours |
| 20°F (29°C) | 22 hours |
| 30°F (34°C) or less | 27 hours |
If you have just received or removed this unit from a climate with temperatures at or below 50°F (10°C), do not open this container until the following conditions are met; otherwise, condensation could occur and damage to the device and/or media may result. Place this package in the operating environment for the time duration according to the temperature chart.
As you can see from this table, you must place a hard disk drive that has been stored in a colder-than-normal environment into its normal operating environment for a specified amount of time to allow it to acclimate before you power it on.
Spindle Motors
The motor that spins the platters is called the spindle motor because it is connected to the spindle around which the platters revolve. Spindle motors in hard disk drives are always connected directly; no belts or gears are involved. The motor must be free of noise and vibration; otherwise, it can transmit a rumble to the platters, which can disrupt reading and writing operations.
The spindle motor also must be precisely controlled for speed. The platters in hard disk drives revolve at speeds ranging from 3,600rpm to 15,000rpm (60250 revolutions per second) or more, and the motor has a control circuit with a feedback loop to monitor and control this speed precisely. Because the speed control must be automatic, hard disks do not have a motor-speed adjustment. Some diagnostics programs claim to measure hard disk rotation speed, but all these programs do is estimate the rotational speed by the timing at which sectors pass under the heads.
There is actually no way for a program to measure the hard disk drive’s rotational speed; this measurement can be made only with sophisticated test equipment. Don’t be alarmed if some diagnostics program tells you that your drive is spinning at an incorrect speed; most likely, the program is wrong, not the drive. Platter rotation and timing information is not provided through the hard disk controller interface. In the past, software could give approximate rotational speed estimates by performing multiple sector read requests and timing them, but this was valid only when all drives had the same number of sectors per track and spun at the same speed. Zoned-bit recordingcombined with the many various rotational speeds used by modern drives, not to mention built-in buffers and cachesmeans that these calculation estimates cannot be performed accurately by software.
On most drives, the spindle motor is on the bottom of the drive, just below the sealed HDA. Many drives today, however, have the spindle motor directly built in to the platter hub inside the HDA. By using an internal hub spindle motor, the manufacturer can stack more platters in the drive because the spindle motor takes up no vertical space.
Fluid Dynamic Bearings
Traditionally, spindle motors have used ball bearings in their design, but limitations in their performance have now caused drive manufacturers to look for alternatives. The main problem with ball bearings is that they have approximately 0.1 micro-inch (millionths of an inch) of runout, which is lateral side-to-side play in the bearings. Although that may seem small, with the ever-increasing density of modern drives it has become a problem. This runout allows the platters to move randomly that distance from side to side, which causes the tracks to wobble under the heads. Additionally, the runout plus the metal-to-metal contact nature of ball bearings allows an excessive amount of mechanical noise and vibration to be generated, and that is becoming a problem for drives that spin at higher speeds.
The solution to this problem came in the form of fluid dynamic bearings, which use a highly viscous lubricating fluid between the spindle and sleeve in the motor. This fluid serves to dampen vibrations and movement, allowing runout to be reduced to 0.01 micro-inches or less. Fluid dynamic bearings also allow for better shock resistance, improved speed control, and reduced noise generation. Today, the majority of hard disks use fluid dynamic bearings, especially the drives that have very high storage capacities of 160GB and up and/or high spindle speeds. The traditional ball bearings are, however, still used in low-cost entry-level drives, but even these will likely be phased out completely in the next few years.
Logic Boards
All hard disk drives have one or more logic boards mounted on them. The logic boards contain the electronics that control the drive’s spindle and head actuator systems and present data to the controller in some agreed-upon form. On ATA drives, the boards include the controller itself, whereas SCSI drives include the controller and the SCSI bus adapter circuit.
Many disk drive failures occur in the logic board, not in the mechanical assembly. (This statement does not seem logical, but it is true.) Therefore, you sometimes can repair a failed drive by replacing the logic board rather than the entire drive. Replacing the logic board, moreover, enables you to regain access to the data on the drivesomething that replacing the entire drive does not provide. Unfortunately, none of the drive manufacturers sell logic boards separately. The only way to obtain a replacement logic board for a given drive would be to purchase a functioning identical drive and then cannibalize it for parts. Of course, it doesn’t make sense to purchase an entire new drive just to repair an existing one, except in the case where data recovery from the old drive is necessary.
If you have an existing drive that contains important data, and the logic board fails, you will be unable to retrieve the data from the drive unless the board is replaced. Because the value of the data in most cases will far exceed the cost of the drive, a new drive that is identical to the failed drive can be purchased and cannibalized for parts such as the logic board, which can be swapped onto the failed drive. This method is common among companies that offer data-recovery services. They will stock a large number of popular drives that they can use for parts to allow data recovery from the defective customer drives they receive.
Most of the time the boards are fairly easy to change with nothing more than a screwdriver. Merely removing and reinstalling a few screws as well as unplugging and reconnecting a cable or two are all that is required to remove and replace a typical logic board.
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