Slower performance with ext4
Chan Chung Hang Christopher
christopher.chan at bradbury.edu.hk
Thu Nov 5 13:34:44 UTC 2009
>> You might want to also do a boot with your ext4 filesystems mounted with
>> 'barrier=0' in fstab.
> Can you explain what this does?
It disables write barriers. Write barriers are enabled by default on
ext4. Blast Mark, making me bone up on what is going on lately. :-)
That means that if write-caches are enabled on disks, you are at risk of
losing data in the event of a sudden power loss but you get better
performance in return. Write barriers allow you to have write-caches
enabled and not have to risk losing data by ensuring that data is safely
on disk before saying "It's done."
However, not everything disk related supports write-barriers, namely
device-mapper, so if you use LVM or any md module other than raid1, you
better turn write-caches off or get yourself a hardware raid card with
bbu cache or a bbu nvram card and data=journal.
More information about the ubuntu-users