NetBSD disk backup over network

[Ivan Voras]

Matthew D. Fuller wrote:

>>You can easily save the stream of updates as a redo log (well,
>>that's the idea I've been running around with).
> 
> Isn't that what the gjournal SoC thing was about?

No, not exactly. The idea was to make a journal of a GEOM device I/O 
requests on a separate device in the attempt to solve filesystem 
journaling, but that didn't work out (actually, gjournal works more or 
less fine, but as far as I understand it, there's a problem similar as 
with SoftUpdates - even if you journal writes on device level with 
filesystem mounted "sync", UFS keeps references to inodes in 
not-entirely-consistent way, so a fsck is always needed after unclean 
shutdown; in other words, UFS journaling must be done on UFS/VFS level, 
not GEOM in order to keep track of metadata semantics).

Something like a filesystem that doesn't do any read caching, and keeps 
ALL data ALWAYS in sync with on-disk state could work with gjournal and 
also with gmirror+geom_gate combination. Such filesystem would probably 
be similar to GFS, AFAIK.