Re: CVS commit: src/lib/libc/sys

[David Holland <dholland-sourcechanges%netbsd.org@localhost>]

On Wed, Mar 25, 2009 at 08:58:18AM +0000, Andrew Doran wrote:
 > > Log Message:
 > > Update the note about sync returning before buffers are written: it is a
 > > piece of historical behavior, not a current bug. Also, while here, add a
 > > bit about disk write-back caches and point to dkctl/scsictl.
 > > Bump date. (first time since 1993!)
 > 
 > Thanks, however:
 > 
 > +.Sh CAUTIONS
 > +Many modern disks contain write-back caches.
 > +In theory
 > +.Fn sync
 > +flushes these.
 > 
 > This is not true, unless you are using logging (or zfs!).

It should be true; why is it not? Does this need to be moved under BUGS?

 > +In practice there are many possible ways for this mechanism to go
 > +astray.
 > +It is prudent (where possible) to allow a few seconds after syncing
 > +for everything to settle before e.g. turning off the power.
 > +.Pp
 > +It may also be desirable to use
 > +.Xr dkctl 8
 > +or
 > +.Xr scsictl 8
 > +to disable the write-back cache entirely.
 > 
 > This is wishy washy. It gives the sense that we know there is a problem, but
 > simply couldn't be arsed fixing it. What do you want to convey?

Should we have a list of filesystems and whether they work properly?
Crossreferences to mount_foo(8) for all foo? Or should it just contain
Kirk's advice, that is, people who care about their data shouhld
always disable the write-back cache?

-- 
David A. Holland
dholland%netbsd.org@localhost