On Tue, Mar 29, 2011 at 11:26 AM, Eric Sandeen <sandeen@xxxxxxxxxx> wrote: > > On 3/29/11 9:05 AM, Theodore Tso wrote: > > > > On Mar 28, 2011, at 2:06 PM, Eric Sandeen wrote: > >> > >> No other fs that I know of enforces this "don't fill the fs to > >> capacity" common sense programatically, though. > > > > Actually, we (ext2) copied this from the BSD Fast File System (FFS) > > which used a default MINFREE of 10%. For ext2 we decided to bring > > it down to 5%. FreeBSD currently uses 8% as their default free > > ratio. > > Clearly I don't know enough filesystems, I guess ;) > > Should have said "linux filesystem" perhaps. > > > The decrease does seem to be relative to the percentage of free > > space, from empirical experience, although no one I know of has done > > a formal analysis of the slowdown. A lot depends on your workload, > > how much memory pressure you place on your system, etc. I've > > actually started seeing slowdowns starting as early as 80% full when > > you're trying to allocate large chunks (1M to 8M) at a time, although > > this isn't something where I've gathered hard data; just what I've > > noticed from looking at different systems and their performance > > characteristics. > > > > Fortunately disks are cheap, and lots of people end up buying far > > more disk space than they need, and so they naturally keep their file > > systems well under 75-80% full. > > > > If someone wants to add some tuning parameters to mke2fs.conf, so > > they can set their own personal default free ratios, or even > > min_reserved_blocks and max_reserved_blocks settings, that's probably > > a reasonable patch to e2fsprogs that I'd be willing to accept. > > Hm I thought I had sent that, but it was only for the other two > semi-controversial behaviors. :) > > I agree, it seems like at least a decent first step to make it > more site/admin-configurable. > > -Eric > Thanks all for the informative replies. I never meant to suggest that 5% is a bad default as a general matter (but I dropped the ball communicating that); I agree entirely that non-root users should not be able to degrade performance by filling up the disk and that 5% is a very good default choice. My only (admittedly unsupported) claim was that past some **fixed** value there is little gain from reserving more space independently of the size of the volume. When I get a chance, I will try to design a benchmark to test that claim (having a few spare 12TB volumes helps) but I fear the results will depend heavily on the usage pattern. Oren Elrad Dept. of Physics Brandeis University -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
