On 2017-09-14 03:54, Duncan wrote:
Austin S. Hemmelgarn posted on Tue, 12 Sep 2017 13:27:00 -0400 as
excerpted:
The tricky part though is that differing workloads are impacted
differently by fragmentation. Using just four generic examples:
* Mostly sequential write focused workloads (like security recording
systems) tend to be impacted by free space fragmentation more than data
fragmentation. Balancing filesystems used for such workloads is likely
to give a noticeable improvement, but defragmenting probably won't give
much.
* Mostly sequential read focused workloads (like a streaming media
server)
tend to be the most impacted by data fragmentation, but aren't generally
impacted by free space fragmentation. As a result, defrag will help
here a lot, but balance won't as much.
* Mostly random write focused workloads (like most database systems or
virtual machines) are often impacted by both free space and data
fragmentation, and are a pathological case for CoW filesystems. Balance
and defrag will help here, but they won't help for long.
* Mostly random read focused workloads (like most non-multimedia desktop
usage) are not impacted much by either aspect, but if you're on a
traditional hard drive they can be impacted significantly by how the
data is spread across the disk. Balance can help here, but only because
it improves data locality, not because it compacts free space.
This is a very useful analysis, particularly given the examples. Maybe
put it on the wiki under the defrag discussion? (Assuming something like
it isn't already there. I've not looked in awhile.)
I've actually been meaning to write up something more thoroughly about
this online (probably as a Gist). When finally get around to that
(probably in the next few weeks), I'll try to make sure a link ends up
on the defrag page on the wiki.
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
