On Tue, Sep 28, 2010 at 02:53:46PM -0400, Ivan.Novick@xxxxxxx wrote: > Hi all, > > According to the documentation the allocsize mount option: "Sets the > buffered I/O end-of-file preallocation size when doing delayed allocation > writeout" > > Will this value limit "extent" sizes to be be no smaller than the allocsize? No - it's specualtive preallocation. > I have set the following mount options: > (rw,noatime,nodiratime,logbufs=8,allocsize=512m) /me wishes he could run a sed script across the internet. noatime implies nodiratime, and logbufs=8 is the default, so you only need "noatime,allocsize=512m" > And yet, depending on the workload, the extent sizes are often 1 or 2 orders > of magnitude lower than 512 MB ... It's speculative and there's no guarantee that it can find a big enough extent to complete the full allocsize allocation. Also, when you close the file the speculative allocation beyond EOF is truncated away. This is a particular problem with NFS servers. > If I wanted to do further reading on the subject, can someone point me to an > approximate location in the code where the size of a newly created extent is > determined? Start here: fs/xfs/xfs_iomap.c::xfs_iomap_write_delay() Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
