Path: utzoo!utgpu!watmath!att!bellcore!rutgers!bpa!cbmvax!daveh From: daveh@cbmvax.UUCP (Dave Haynie) Newsgroups: comp.sys.amiga Subject: Re: FFS details Message-ID: <7686@cbmvax.UUCP> Date: 17 Aug 89 15:34:19 GMT References:Distribution: comp Organization: Commodore Technology, West Chester, PA Lines: 33 in article , cire@dustbin.cisco.com (Eric B. Decker) says: > Xref: cbmvax comp.sys.amiga:41248 comp.sys.amiga.tech:7424 > 1) How does the FFS deal with data integrity? Is there some kind of > checksum or other protection mechanism? There are checksums on file, directory, and extension blocks under FFS, but not on data blocks. These checksums, I suppose, are mainly there for historical reasons if anything. The responsibility for checking data is considered the domain of the device driver, not the filesystem. So for floppies, for instance, there will be checksum information on hidden blocks outside of the 512 byte DOS managed block. For SCSI hard drives, data checking is managed by the drive itself; even the device driver doesn't see any of that. > 2) Where can I find detailed specifications of the FFS? Not sure about that one. The specs on the Standard FileSystem are in the AmigaDOS Technical Reference Manual, which is now part of the large AmigaDOS book you find in book and computer stores. It's not written very well, but most of the information on SFS is there. FFS from a low-level point of view is very much like SFS, only the data blocks store only data; the checksum and parent/next links have been removed. At a higher level, FFS is much smarter about the block allocations is makes. I've hacked around with the disk format since 1985, so I can probably answer any related specific questions. > Eric B. Decker -- Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: D-DAVE H BIX: hazy Be careful what you wish for -- you just might get it