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I was reading trough the link on journaling-filesystems and i would like to know where exactly is the journal stored in my Harddisk.

Some pointers on this image shown below
alt text

Thanks,
Sen

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2 Answers 2

up vote 6 down vote accepted

The journal is stored in a separate space of the partition, you cannot access it directly. You can use sudo debugfs /dev/sda# where the # symbol is the number of your partition, and then using logdump in debugfs to print it out. The output is confusing though.

Generally, as a regular user, you don't need to know about the journal. Using ext3/4 will be sufficient to prevent data loss (in most cases).

This link might help: http://www.linuxforums.org/forum/red-hat-fedora-linux/121074-ext3-journal.html

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Thanks Evgeny.. –  Sen Nov 25 '10 at 9:33
    
I just wanted to know, as it was stated in the link, what is this on-disk journal? Where is it in the HDD? That picture was a bit confusing to me. –  Sen Nov 25 '10 at 9:35
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There is no fixed place for the journal, each filesystem stores it in a different place.

If you are expecting it to be a regular file, then your are mistaken, it's more like a part of the filesystem structure like the inode table. The funny point is that ext3/4 treats it exactly like a regular file. It is usually found in the inode number 8, but this is a kernel parameter that can be changed at compile time.

If you want to get technical, this is great read about the ext3 structure. If you don't mind put journal in a place with words like partition table, inode or block and don't worry about it.

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Good comment.. would like to vote up but lack of points.. :-) –  Sen Nov 25 '10 at 9:39
    
"It is usually found in the inode number 8", can you explain briefly on this to me? –  Sen Nov 25 '10 at 9:40
    
yup.. i found it.. it is the inode number of the Journal file.. –  Sen Nov 25 '10 at 9:45
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