Dave Chinner - 05.09.18, 00:23: > 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. Yeah. It was interesting to see that neither the CPU nor the SSD was fully utilized during that time tough. > > 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. Great. I saw the recent writeback error discussion as well. Thanks, -- Martin
