Re: dar became very slow (and process in D state?)

Il giorno ven, 17/01/2020 alle 21.32 +0100, Denis Corbin ha scritto:
> 
> On 17/01/2020 12:47, Andrea Vai wrote:
> [...]
> > 
> > I have just tried and didn't make any difference, but I am
> > wondering whether I am not understanding something. My problem
> > appears while writing a new archive, so does --sequential-read
> > option matter as well in that case?
> 
> Yes, you are correct. The sequential-read does nothing (except
> concerning the archive of reference if used) when creating an
> archive.
> 
> The archive is produced by appending data to a file, there still
> might
> be some seek backward if compression is worse than storing data
> uncompressed (operation cp does not do). This one is not possible to
> disable unless you disable compression at all. You can also write
> the
> archive to stdout to avoid having this occuring though dar will try
> and get an error so the system call will still differ from what cp
> would do.
> 
> 	dar -c - .... > my.archive.1.dar
> 
> Another condition that have influence on the way dar writes to an
> archive is when a file has changed, dar will retry saving it up to 3
> times by default. See --retry-on-change option to disable this.
> 
> 
> > 
> > the command I run is
> > 
> > # SECONDS=0; mount UUID=ae7ac0ca-d0bc-46c8-81f1-d2b67e1f95f3
> > /mnt/pendrive && rm -f /mnt/pendrive/aero.1.dar && dar -c
> > /mnt/pendrive/aero -R /home/andrea/Musica/MP3/Aerosmith && umount
> > /mnt/pendrive; echo "Ci ho messo: $SECONDS secondi.
> > 
> > which, as far as I know, doesn't involve reading a catalog, does
> > it?
> 
> You seems doing a full backup (I cannot see whether there is a
> .darrc
> or /etc/darrc but assuming there is none) without compression on
> data
> that do not seem subject to change.

Yes, your assumptions are correct.
And thank you for all the the explanations,

>  So I thus cannot see what dar does
> so differently from the cp command in that context for the first
> trigger the kernel bug while the second does not...

Many thanks,
Ciao :-)
Andrea