On Mar 01, 2009 21:47 -0500, Theodore Ts'o wrote: > This is a reasonable question. What would be great is if we could get > a benchmarking team to fill an ext4 filesystem with files. The simple > thing would be if we did something fixed --- say, 50 files per > directory, each file 100k, and say 10 subdirectories in each > directory, to some fixed depth, and with a filesystem size of at least > 8 gigabytes (which would give us at least 16 flex groups with the > default flex size of 16) --- and then filled each filesystem to from > 0% to 90% in increments of 10%, and from 90% to 99% in increments of > 1%, and then ran some throughput benchmark like bonnie on the mostly > filled filesystem. We've done tests like this, and it is important to take the inner vs. outer cyliners into account. It can happen that even a "perfectly" allocated filesystem will appear to show slowdowns in performance as it gets full, yet this is partitially due to physical disk layout issues. > A better filler would probably use a random file sizes with a average > size of say 64k, but with outliers from 4k to 128 megs, and a similar > random distribution of number of files per directory, and number of > subdirectories and depth of subdirectories. You describe the Reiserfs "Mongo" benchmark. > I suppose it would be good to do one set of charts with a filesystem > size of 8 gigs, and another at 80 gigs and 800 gigs, and see if the > shape of the filesystem curve changes at scale. Once we have that, we > would be in a position to make a reasonable set of defaults. > > Or we could just guess and come up with some percentage figure that > sounds good. :-) I suspect that at a certain filesystem size, there isn't much benefit in having more reserved space. If we keep 50GB of reserved space then this is likely to contain a decent amount of 1MB free chunks, which is what we really care about. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc. -- 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
