Hello, I recently ran into the subdirectory scalability issue of ext3 on our listserver. Thankfully, ext4 exists, so it was finally time to move to it. I followed the published process to convert the ext3 filesystem to ext4[0] and things worked well, I'm no longer hitting the 32000 limit on subdirectories. However, ever since I did that change, I've noticed an increase in I/O wait state on the CPUs. I've been trying to determine why, and if there were some things I should tune on this ext4 filesystem. First thing I found was that the Filesystem Features of an ext4 filesystem that were converted from ext3 are different than those that are set on a filesystem that was created as ext4 (on Debian Squeeze), From tune2fs -l: a newly created ext4 has: Filesystem features: has_journal ext_attr resize_inode dir_index filetype needs_recovery extent flex_bg sparse_super huge_file uninit_bg dir_nlink extra_isize my migrated one has: Filesystem features: has_journal ext_attr resize_inode dir_index filetype needs_recovery extent sparse_super large_file uninit_bg The difference being new filesystems have 'flex_bg', 'huge_file' and 'extra_isize' set, and the converted filesystem has 'large_file' and 'uninit_bg'. I'm not sure I understand why the difference and wonder if someone can explain to me why? Or if I should be changing these? Currently the filesystem is mounted with just rw,relatime set, and I wonder if there is a combination of some tune2fs changes, and mount options that we would benefit from. Basically this filesystem has a lot of small files, there is a set of spool directories where there are a lot of small writes, small reads and deletes. There is also an archive of list postings, which is a fairly large set of small files, which is mostly small writes, reads every once and a while. There is also a series of stats that happen on a large number of subdirectories. Thank you for any suggestions! micah 0. https://ext4.wiki.kernel.org/index.php/Ext4_Howto#Converting_an_ext3_filesystem_to_ext4
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