So today I discovered that Red Hat Linux (at least RHEL 4) includes the online ext2 resize support feature in the kernel. This is probably really old news, but it's news to me. This is incredibly useful (as long as it's safe, which I'm sure it is if Red Hat is including it by default). We've been using reiserfs on all our boxes that have LVM configured since support for online resizes for ext2 filesystems seemed like it involved more work than necessary. The syntax is similar to resize_reiserfs too.

ext2online -v /dev/VG01/LV01

This will extend the filesystem to fill the partition (by default, but you can specify a size if you wanted). I tested it out and it appears to handle large resizing just as easily as smaller resizing. I ran a dd command to write blocks to the partition while it was resizing and it had absolutely no visible difference. I'm stoked!