We have a filesystem, on LVM, created as ext2 - and in daily use running 8-10 webservers (software, tempfiles, logfiles).
The discs are "local" to the OS, but are really SAN disks provided to the VmWare ESX server. Our "server" is a virtual server running RedHat 6.
The disk size is 56GB, about 26GB usage (varies).
The log files are the most active, and ranges from some 10kb up to 2GB.
Lifetime writes (since august 2012) are about 23 TB (yes, Tera) according to tune2fs.
With regards to the filesystem (not the process) - What would be the pros and cons with upgrading from ext2 to ext4 vs creating av new filesystem as ext4, copying and switching to the new disk?
We will go to ext4, and will probably create a new fs and copy - since disk is not an issue, but will an upgrade give us the same - and will files and directories created before the upgrade be changed?
If there will be a difference between the old and the new files: What will de difference be?
If you can afford it (downtime and temporary disk space), creating new ext4 and copying data would be much better.
Some of ext4 features can be enable only on format (example flex_bg, support for >16TiB), but even more than that, only new files will be created using much more efficient extents (as opposed to list of blocks in direct, indirect, double-indirect, and triple-indirect lists). Also ext4 has more efficient allocation of disk space (which impacts performance), so going with fresh filesystem will get you gains there too. Not to mention to format/copy will also defragment your old filesystems for free.
Upgrade info and related issues can be found at Ext4 HOWTO