On Tue, Sep 04, 2018 at 05:36:43PM +0200, Martin Steigerwald wrote: > Dave Chinner - 04.09.18, 02:49: > > On Mon, Sep 03, 2018 at 11:49:19PM +0100, Richard W.M. Jones wrote: > > > [This is silly and has no real purpose except to explore the limits. > > > If that offends you, don't read the rest of this email.] > > > > We do this quite frequently ourselves, even if it is just to remind > > ourselves how long it takes to wait for millions of IOs to be done. > > Just for the fun of it during an Linux Performance analysis & tuning > course I held I created a 1 EiB XFS filesystem a sparse file on another > XFS filesystem on an SSD of a ThinkPad T520. It took several hours to > create, but then it was there and mountable. AFAIR the sparse file was a > bit less than 20 GiB. Yup, 20GB of single sector IOs takes a long time. > Trying to write more data to it than the parent filesystem can hold back > then resulted in "lost buffer writes" or something like that in > kernel.log, but no visible error message to the process that wrote the > data. That should mostly be fixed by now with all the error handling work that went into the generic writeback path a few kernel releases ago. Also, remember that the only guaranteed way to determine that there was a writeback error is to run fsync on the file, and most applications don't do that after writing their data. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
