slave zone files unreadable

[Mark Andrews]

In message <barmar-79D854.20233411072014 at news.eternal-september.org>, Barry Margolin writes:
> In article <mailman.559.1405100971.26362.bind-users at lists.isc.org>,
>  Evan Hunt <each at isc.org> wrote:
> 
> > On Fri, Jul 11, 2014 at 12:12:22PM -0400, John Wobus wrote:
> > > In cases analogous to this, software often saves both
> > > text and binary, and when initializing, uses mtime to
> > > decide whether it can safely use the binary.  Some resources
> > > are spent storing the extra file and admins have yet
> > > another way to screw things up, but the strategy
> > > does have benefits.
> > 
> > You can't always rely on mtime for that.  The disk may have been hit by
> > cosmic rays since last time you read the file, and mtime hasn't changed but
> > the file is different anyway.
> 
> BIND already assumes mtime is reliable -- if you do "ndc reload", it 
> only reloads zone files whose mtimes are newer than when the zone was 
> previously loaded.
> 
> If you're worried about cosmic rays, you can't rely on ANYTHING on the 
> disk. Why would you consider the file contents to be reasonable if they 
> could change spontaneously.
> 
> Anyway, don't all modern disks have ECC codes in them? These will detect 
> and correct bit flips in the mtime just as well as the contents. If you 
> want extra safety, use RAID.

The real problem is humans.  They like to tinker with files (hence
the subject line).  There really shouldn't be a reason for anyone
to need to read slave database files.  They are there so named can
have the zone content when it starts up rather than having to
re-transfer the content at startup.  If you need the contents of the
zone axfr them from the server.  That way you actually get up to
date content not 15 minute old content.

If we could get people away from wanting to use a editor on master
files directly we would.  The practice is highly error prone even
for experts.

> -- 
> Barry Margolin
> Arlington, MA
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org