Converting ext3 to ext4 - results (Re: ext3 vs ext4)

[Nathan England]

one of the articles I read yesterday says the initial fsck of a drive will 
take as long as a normal fsck on ext3, then subsequent fsck'ing will be 
faster...

http://kernelnewbies.org/Ext4#head-9a25213c5b924bdb8b33efbcb91bfa1279bd2b00

~~ From the article ~~

Fsck is a very slow operation, especially the first step: checking all the 
inodes in the file system. In Ext4, at the end of each group's inode table will 
be stored a list of unused inodes (with a checksum, for safety), so fsck will 
not check those inodes. The result is that total fsck time improves from 2 to 
20 times, depending on the number of used inodes 
(http://kerneltrap.org/Linux/Improving_fsck_Speeds_in_Ext4). It must be 
noticed that it's fsck, and not Ext4, who will build the list of unused 
inodes. This means that you must run fsck to get the list of unused inodes 
built, and only the next fsck run will be faster (you need to pass a fsck in 
order to convert a Ext3 filesystem to Ext4 anyway). There's also a feature that 
takes part in this fsck speed up - "flexible block groups" - that also speeds 
up filesystem operations.

- nathan