On Tue, 2009-01-20 at 09:19 -0500, erik quanstrom wrote:
> > > in the case of zfs, my claim is that since zfs can reuse blocks, two
> > > vdev backups, each with corruption or missing data in different places
> > > are pretty well useless.
> >
> >
> > Got it. However, I'm still not fully convinced there's a definite edge
> > one way or the other. Don't get me wrong: I'm not trying to defend
> > ZFS (I don't think it needs defending, anyway) but rather I'm trying
> > to test my mental model of how both work.
>
> if you end up rewriting a free block in zfs, there sure is. you
> can't decide which one is correct.
You don't have to "decide". You get use generation # for that.
> > P.S. Oh, and in case of ZFS a damaged vdev will be detected (and
> > possibly re-silvered) under normal working conditions, while
> > fossil might not even notice a corruption.
>
> not true. one of many score checks:
>
> srv/lump.c:103: seterr(EStrange, "lookuplump
> returned bad score %V not %V", u->score, score);
I don't buy this argument for a simple reason: here's a very
easy example that proves my point:
term% fossil/fossil -f /tmp/fossil.bin
fsys: dialing venti at net!$venti!venti
warning: connecting to venti: Connection refused
term% mount /srv/fossil /n/f
term% cd /n/f/test
term% echo 'this is innocent text' > text.txt
term% cat text.txt
this is innocent text
term% dd -if /dev/cons -of /tmp/fossil.bin -bs 1 -count 8 -oseek 278528 -trunc 0
this WAS
8+0 records in
8+0 records out
term% rm /srv/fossil /srv/fscons
term% fossil/fossil -f /tmp/fossil.bin
fsys: dialing venti at net!$venti!venti
warning: connecting to venti: Connection refused
create /active/adm: file already exists
create /active/adm adm sys d775: create /active/adm: file already exists
create /active/adm/users: file already exists
create /active/adm/users adm sys 664: create /active/adm/users: file already
exists
nuser 5 len 84
term% mount /srv/fossil /n/f2
term% cat /n/f2/test/text.txt
this WAS innocent text
term%
Of course, with ZFS, the above corruption would be always
noticed and sometimes (depending on your vdev setup)
even silently fixed.
Thanks,
Roman.
