Thursday, 14 April 2011

Filesystem Journaling

Journal Options

There are 3 possible settings for Journaling. They are ordered, journal and writeback

These can be set at mount time
#mount -o data=TYPE

ordered is the default and writes only the metadata

journal writes metadata and data at the same time

writeback is just metadata but there is no garuntee on commits

It is also possible to change the frequency of journal commits, the default is 5 seconds
#mount -o commit=30

Journal Placement

It is possible to put the journal on another device which can improve performance

remove the journal
#tune2fs -O ^has_journal /dev/sda1

Create the external journal
#mkfs -O journal_dev -b blocksize /dev/sdb1

Tell the FS to use the new journal
#tune2fs -j -J device=/dev/sdb1 /dev/sda1

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