Re: [ext4] Documentation patch

From: Theodore Tso
Date: Sun Dec 07 2008 - 15:32:15 EST

Good points. OK, how about this?

- When comparing performance with other filesystems, it's always
important to try multiple workloads; very often a subtle change in a
workload parameter can completely change the ranking of which
filesystems do well compared to others. When comparing versus ext3,
note that ext4 enables write barriers by default, while ext3 does
not enable write barriers by default. So it is useful to use
explicitly specify whether barriers are enabled or not when via the
'-o barriers=[0|1]' mount option for both ext3 and ext4 filesystems
for a fair comparison. When tuning ext3 for best benchmark numbers,
it is often worthwhile to try changing the data journaling mode; '-o
data=writeback,nobh' can be faster for some workloads. (Note
however that running mounting with data=writeback can potentially
leave stale data exposed in recently written files in case of an
unclean shutdown, which could be a security exposure in some
situations.) Configuring the filesystem with a large journal can
also be helpful for metadata-intensive workloads.

- Ted
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