cire@dustbin.cisco.com (Eric B. Decker) (08/17/89)
I am dealing with a hard disk problem that is formated using the Fast File System. I know almost nothing about FFS and have no documentation for it. I have lots of other documentation but not that stuff. One of the things I was wondering is how does it ensure data integrity. So my two questions are 1) How does the FFS deal with data integrity? Is there some kind of checksum or other protection mechanism? 2) Where can I find detailed specifications of the FFS? Thanks, -c -- cire|eric Eric B. Decker Token Ring Development cisco Systems - engineering Menlo Park, California email: cire@cisco.com uSnail: 1360 Willow Rd., Menlo Park, CA 94025 Phone : (415) 326-1941
daveh@cbmvax.UUCP (Dave Haynie) (08/17/89)
in article <CIRE.89Aug16133920@dustbin.cisco.com>, 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
lphillips@lpami.wimsey.bc.ca (Larry Phillips) (08/18/89)
In <CIRE.89Aug16133920@dustbin.cisco.com>, cire@dustbin.cisco.com (Eric B. Decker) writes: >2) Where can I find detailed specifications of the FFS? I don't know of anywhere you can find the details offhand, but here are all the differences I know of between the old and new file system. -------------------- Block 0 (Cyl 0, Head 0, Sector 0 on any partition), contains: OFS: 'DOS',0 FFS: 'DOS',1 -------------------- Root block: FFS can have an extension to the bitmap pointer table. The pointer to the next sector containing pointers to bitmap pages is contained in longword $68 -------------------- Hash chain extensions are sorted in increasing order of blocks pointed to. -------------------- File data blocks contain 512 bytes of data, with none of the overhead contained in the OFS scheme. This results in a tradeoff. You trade considerable speed for less recoverability. -------------------- -larry -- "So what the hell are we going to do with a Sun?" - Darlene Phillips - +-----------------------------------------------------------------------+ | // Larry Phillips | | \X/ lphillips@lpami.wimsey.bc.ca -or- uunet!van-bc!lpami!lphillips | | COMPUSERVE: 76703,4322 -or- 76703.4322@compuserve.com | +-----------------------------------------------------------------------+
new@udel.EDU (Darren New) (08/22/89)
For various reasons, I wish to write a variant of DiskCopy except that it would work on my SCSI hard drive. Can anyone direct me to the sources for a program that can inhibit, read, and write through the device driver (not the scsi.library) and that is PD, FD, ShareWare, etc? I have the Fish disks up to 196 or so. The only programs I've seen only work on floopies. I have the info I need on the FFS (from the manual of the DiskMechanic program, which I strongly disrecommend). Thanks in advance -- Darren