graeme@omero.enet.dec.com (Graeme Harker) (03/22/90)
In article <384@vela.acs.oakland.edu> schemers@vela.acs.oakland.edu (Roland Schemers III) writes: > Hello! I have a question about using 'dump'. How dangerious is it to > dump an active file system? That is, dumping a file system that is > mounted, and while the system is in multi-user mode? I have gotten > various replies from DEC, ranging from "It might corrupt the whole dump", > or "Only the active files will be messed up". The "problem" with dump is that for performance reasons it uses the raw interface the the disk and thereby skips the file system buffer and inode cache. Anything in the cache will not be saved by dump. Notice that doesn't just mean that you will dump "old" versions, you risk dumping inconsistent files that have been updated in the cache and only partially flushed to disk. You will see inconsistencies at block boundaries and bad inode information. Consequently dumping a live file system should be avioded wherever possible. However in either of the following conditions a live file system can be dumped with 100% safety: a) the partition has been mounted read-only b) the machine is completely quiet and the buffer cache has been sync-ed If your partition is mounted read-write and you can neither go single-user nor guarantee a quiet machine, I suggest you pick a time of the day when the machine is at its quietest and sync the disk before dumping (and take out an insurance policy). Graeme Harker, Digital SpA, Piazza XX Settembre, 21100 Varese, Italia uucp : ...{sun,decvax,hplabs,ucbvax}!decwrl!omero.enet!graeme Internet : graeme@omero.enet.dec.com Enet : OMERO::GRAEME DECstop : VAR Tel : (+39) 332 298332 DTN : 787-8332