Low-Level Format (LLF)
【转载至】Compguys TechWeb TSP
Why it can be not such a good idea....
Sector header and trailer information is written or updated only during the low-level format (LLF) operation. During normal read and write activity, only the 512 bytes plus the CRC (Cyclic Redundancy Check) bytes in the trailer are written in a sector. Temperature-induced dimensional changes in the drive platters during read and write operations can become a problem.
When a 5 1/4-inch platter drive is low-level formatted five minutes after powerup at a relatively cold platter temperature of 70° F, the sector headers and trailers and the 512-byte dummy data values are written to each track on each platter at specific locations.
Suppose that you save a file on a drive that has been running for several hours at a platter temperature of 140° F. The data areas of only several sectors are updated. But with the drive platters as much as 70° warmer than when the drive was formatted, each aluminum drive platter will have expanded in size. Each track, therefore, would have moved outward a distance of approximately 1.25 thousandths of an inch. Most 5 1/4-inch hard disks have track densities between 500 and 1,000 TPI (tracks per inch), with distances of only 1 to 2 thousandths of an inch between adjacent tracks. As a result, the thermal expansion of a typical 5 1/4-inch hard disk platter could cause the tracks to migrate from one-half to more than one full track of distance below the heads. If the drive head-movement mechanism does not compensate for these thermally induced dimensional changes in the platters, severe mistracking results.
When mistracking occurs, the data areas in each sector that have been updated at the higher temperature fail to line up with the sector header and trailer information. If the sector header and trailer information cannot be read properly, DOS usually issues an error message like this one:
Sector not found reading drive C
Abort, Retry, Ignore, Fail?
The data is misaligned with the sector boundaries on those tracks. This thermal effect also can work in reverse: If the drive is formatted and written to while it is extremely hot, it may not read properly while cold because of dimensional changes in the platters. This problem occurs with drives that have the "Monday-morning blues," in which they spin but cannot read data properly when they are first powered on, especially after being off for an extended period (over a weekend, for example). If you leave the power to the system on for some time so that the drive can warm up, the system then may boot and run normally.
If this happens, the next step is to back up the drive completely and initiate a new LLF at the proper operating temperature. This procedure enables the drive to work normally again until temperature-induced mistracking becomes great enough to cause the problem again.
Tip:
Leave the system's power on for at least 30 minutes before performing an LLF on its hard disk. This step ensures that the platters are at a normal operating temperature and have stabilized dimensionally.Knowing that temperature fluctuations can cause mistracking. If possible, allow a system some time to warm up after power-on before storing any data on the hard disk. This procedure is not required for voice coil drives. If you have a cheap stepper motor drive that consistently exhibits temperature-related mistracking problems, you may want to consider running the drive constantly. Doing so would extend its trouble-free life span significantly because the temperature and dimensions of the platters would stay relatively constant.
Modern voice coil actuator drives do not exhibit these dimensional instabilities due to thermal expansion and contraction of the platters because they have a track-following servo mechanism. As the tracks move, the positioner automatically compensates. Many of these drives undergo a noticeable thermal compensation sequence every five minutes or so for the first 30 minutes after being powered on, and usually every 30 minutes after that. During these thermal-compensation routines, you hear the heads move back and forth as they measure and compensate for platter-dimension changes.
Note:Some Manufacturers of Hard Drives state that attempting to properly Low-Level Format your Hard Drive will void any existing manufacturer's warranty, and recommend that Hard Drives be returned to tne manufacturer for any required Low-Level Formatting. So if your smart you'll contact them first.
