Questions regarding journal replay

[Ralf Hildebrandt]

Today, I had to uncleanly shutdown one of our machines due to an error
in 2.6.28.3. Durin the boot sequence, the ext4 partition /home
experienced a journal replay. /home looks like this:

/dev/mapper/volg1-logv1 on /home type ext4 (rw,noexec,nodev,noatime,errors=remount-ro)

Filesystem              Size  Used Avail Use% Mounted on
/dev/mapper/volg1-logv1 2,4T  1,4T 1022G  58% /home

Filesystem                Inodes   IUsed   IFree IUse% Mounted on
/dev/mapper/volg1-logv1 19519488 8793310 10726178   46% /home

The journal replay too quite a while. About 800 seconds.

# dumpe2fs -h /dev/mapper/volg1-logv1
dumpe2fs 1.41.3 (12-Oct-2008)
Filesystem volume name:   <none>
Last mounted on:          <not available>
Filesystem UUID:          032613d3-6035-4872-bc0a-11db92feec5e
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal resize_inode dir_index filetype needs_recovery extent sparse_super large_file uninit_bg
Filesystem flags:         signed_directory_hash 
Default mount options:    (none)
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              19519488
Block count:              624605184
Reserved block count:     0
Free blocks:              267655114
Free inodes:              10726118
First block:              0
Block size:               4096
Fragment size:            4096
Reserved GDT blocks:      875
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         1024
Inode blocks per group:   32
Filesystem created:       Tue May  8 21:04:31 2007
Last mount time:          Thu Feb  5 11:08:27 2009
Last write time:          Thu Feb  5 11:08:27 2009
Mount count:              12
Maximum mount count:      -1
Last checked:             Sat Dec 27 23:16:47 2008
Check interval:           0 (<none>)
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:		            128
Journal inode:            8
First orphan inode:       17529831
Default directory hash:   tea
Directory Hash Seed:      44337061-e542-44bb-afb9-40597ccf1c6d
Journal backup:           inode blocks
Journal size:             128M

Questions:
==========

* Why does it take so long?
* What happens during that time?
* Is my journal maybe too big?

-- 
Ralf Hildebrandt                                Ralf.Hildebrandt at charite.de
Charite - Universitätsmedizin Berlin            Tel.  +49 (0)30-450 570-155
Geschäftsbereich IT | Abt. Netzwerk             Fax.  +49 (0)30-450 570-962
Hindenburgdamm 30 | 12200 Berlin