[OpenAFS] long delay in vos examine

Jeffrey Hutzelman jhutz@cmu.edu
Sun, 04 Dec 2005 20:33:30 -0500

On Friday, November 04, 2005 11:04:15 AM -0700 "Kristen J. Webb" 
<kwebb@teradactyl.com> wrote:

> Hi Everyone,
> I'm seeing a 10-15 minute delay from the
> time I modify a volume to when vos e shows
> me the correct Last Update time.  fs checkv/flushv
> doesn't seem to help.  Looking at the volume
> from another system shows the same delay.

That's right.  We introduced a change late in the 1.3.x series which 
prevents the fileserver from doing an expensive sync operation every time
someone tries to examine a volume (via examine, listvol, etc).  As a 
result, the volume header on disk is updated only when the fileserver would 
have done so anyway.  That will happen immediately for certain kinds of 
changes, every so many new vnode creations, and after an interval of time 
if there is an uncommitted change.  The volume header is also synced any 
time the volume is attached by the volserver for a "real" operation, like a 
move, dump, etc (only list and examine do the silent "peek" attach).

The longest delay there can be between a "trivial" change like touching the 
mod time of an existing file and when the volume header reflects the change 
is 25 minutes.

Note that if you are trying to determine whether to do a backup of a 
volume, you should be looking at the backup volume you are actually going 
to dump, not the read/write volume which may have changed since the backup 
was cloned.  The timestamps on the backup volume will always reflect the 
state of that volume, since a clone or reclone forces the volume header to 
be synced, and backup volumes cannot be changed at any other time.

-- Jeff