COMBINED SAT-GLIDE TEST FOR DASD MANUFACTURING AND IN-SITU OPERATION
Original Publication Date: 1999-Nov-01
Included in the Prior Art Database: 2003-Jun-19
This invention is related to the field of detecting, mapping, and/or failing hard disk drives with potentially damaging surface cluster defects. The method described, called SATGLIDE, merges the current continuous modulation detection (CMD) glide test into the surface analysis test (SAT). The use of subsampling in a pre-SATGLIDE test singles out disk drives with failing characteristics. The pre-SATGLIDE test speeds up the overall SATGLIDE test and reduces its overall cost. The method also shows a simple way to depopulate a disk drive. Currently there are two separate tests that require two separate and expensive testers to perform glide and SAT. This invention solves the problem of interpreting SAT data in terms of head-disk interaction. Currently, SAT is used to determine areas on the surface of a magnetic disk that are unsuitable for recording data. The unusable areas are mapped out so that spare areas are used instead of the defective areas. In present SAT algorithms, it is not possible to determine the nature of a defect. That is, it is not known if the defect is causing head-disk contact or if the defect is solely magnetic in nature. If a defect is causing head-disk contact, then this is a reliability concern and the disk should be replaced rather than having an area simply reassigned. Subsampling is used in the context of this invention disclosure as only testing every Nth cylinder in a disk drive. The use of subsampling in a pre-SATGLIDE test quickly separates out disk drives with failing SATGLIDE characteristics. Since disk drives with surface damage will have SAT clusters, which have spatially low frequency characteristics, they can reliably be detected by subsampling. The pre-SATGLIDE test speeds up the overall SATGLIDE test and reduces its overall cost. Those disk drives that pass the pre-SATGLIDE test will proceed with the normal SAT-test. Glide testing, (CMD), has been used to determine the physical nature, i.e., pit or bump, of the defect. Defects causing intermittent contact between head and disk are very detrimental to safe and reliable DASD operation. The current CMD test uses a subsampling approach by testing only Nth cylinder. Ever since drive-level glide testing for DASD was invented, it has been performed prior to SAT. The reasons for this are at least two-fold. First, it was always felt that SAT does not have the ability to discriminate between different types of defects.