Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!visix!news From: kent@visix.com (Ken Turner) Newsgroups: comp.sys.mac.hardware Subject: Re: SCSI Hard Disk's and Bad Sector Maps Keywords: scsi Message-ID: <1991Apr8.143927.2497@visix.com> Date: 8 Apr 91 14:39:27 GMT References: Sender: news@visix.com Reply-To: kent@visix.com (Ken Turner) Distribution: comp Organization: Visix Software Inc., Reston, Virginia Lines: 44 In article , steveh@tasman.cc.utas.edu.au (Steven Howell) writes: > > I have been curious to were they store the information concerning bad > sectors on scsi, mainly macintosh, drives. I have researched by myself with no > external help, on various drives, going thru their roms, but still cannot > find a bad sector map. The drives i am mailny interested in are Quantum, Sony > and Rodime. I have few drives with bad blocks and wish to map them out. > SCSI drives have a built-in defect list. It can be accessed using the `Read Defect Data' SCSI command. (The actual op-code escapes me.) The list is usually divided into two parts: the production defect list, installed at the factory, and the `grown' defect list, constructed over the lifetime of the drive. The driver that comes with your Macintosh drive is primarily responsible for mapping out bad sectors, using the `Reassign' SCSI command. If it encounters a media error while reading or writing, it should automatically do this, completely invisble to the user. (This is referred to as `on the fly' defect handling by some vendors.) Many vendors also provide a limited test capability with their utility software. It scans the entire drive for defects and then reassigns them. If you have a drive and it has an un-reassigned defect, there are several possibilities. The driver installed might not automatically reassign bad blocks. (I know Rodime's software does, however.) Or, the defect list might be full and no more can be reassigned. Most moderate capacity drives max out at 50-100 defects. Or, most likely, there is some other drive error occuring (like a seek error) that is not a direct result of a physical defect in the disk platter and will not cause the sector to be reassigned. I know it's drastic, but a low-level format sometimes helps in these cases. Ken Turner Visix Softare Inc. kent@visix.com