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<div class="moz-cite-prefix"><tt>Things are progressing well with
the SSD cache feature, so I'd like to give a brief update.</tt><tt><br>
</tt><tt><br>
</tt><tt><tt>dm-cache & bcache<br>
-----------------<br>
Initially both dm-cache and bcache were in scope to provide
users with the SSD caching feature in Fedora 20. Both are
supported by the latest Linux kernels, but unfortunately
userspace tooling (lvm2) for dm-cache still requires
considerable effort so focus has been te have bcache in F20.<br>
<br>
</tt>System wide or Self contained?<br>
------------------------------<br>
For F20 the intention was to have SSD cache Self contained, and
to have it System wide in F21. Looks like we're ahead of
schedule! Thanks to the great cooperation of community members
responsible for other Fedora packages, we may see a well
integrated bcache implementation in F20. Because bcache is quite
new we should however consider it Experimental!<br>
<br>
</tt><tt>What works?</tt><tt><br>
</tt><tt>-----------</tt><tt><br>
</tt><tt>Currently I'm running my root FS on bcache. My system
runs great. Both kernel updates and other updates (in F20
updates-testing*) work without any problems. This means dat a
working intramdisk is created by dracut, which in turn means
that util-linux (blkid) detects bcache. To 'complicate' testing
I have the root FS on lvm (which is on bcache)! And as a bonus
of course I'm experiencing a nice performance :-)<br>
<br>
Because Anaconda doesn't support bcache (yet) creating a running
system with root FS on bcache requires some "manual work", but
once it's running it's running well!<br>
<br>
*) some packages are not yet in updates testing, details below.<br>
<br>
Testing<br>
-------<br>
Thanks to Igor Gnatekno a Fedora Test day is planned 13th of
october: <a class="moz-txt-link-freetext" href="https://fedorahosted.org/fedora-qa/ticket/415">https://fedorahosted.org/fedora-qa/ticket/415</a>. To
support this a Wiki page (work in progress) is maintained:
<a class="moz-txt-link-freetext" href="https://fedoraproject.org/wiki/Test_Day:2013-10-13_SSD_Cache">https://fedoraproject.org/wiki/Test_Day:2013-10-13_SSD_Cache</a>.
Anybody interested in testing is welcome!<br>
<br>
</tt><tt>util-linux<br>
----------<br>
libblkid in util-linux v2.24 will support bcache, which means
that both blkid and wipefs will detect (and wipe) bcache.
Currently util-linux v2.23 is available, but v2.24 rc will be in
F20 (thanks Karel Zak). To test bcache I'm running a patched
v2.23 that already has the planned support for bcache.<br>
<br>
</tt><tt>bache-tools</tt><tt><br>
</tt><tt>-----------</tt><tt><br>
</tt><tt>The bcache-tools package is available in F20
updates-testing, and seems to be in pretty good shape (thank you
reviewers, thanks Hans de Goede</tt><tt>). Currently
bcache-tools includes a bcache-probe utility, but that may no
longer be in the package when F20 is released because it's
obsoleted by blkid in util-linux v2.24.<br>
</tt><tt><br>
</tt><tt>dracut</tt><tt><br>
</tt><tt>------</tt><tt><br>
</tt><tt>Dracut now has a bcache module to build initramfs</tt><tt>
(thanks Harold Hoyer). This works very well, but it currently
needs </tt><tt>the -N option. When util-linux v2.24 is released
dracut will detect bcache and be able to operate without the -N
option.<br>
<br>
LVM2<br>
----<br>
LVM2 does normally not accept a bcache device as PV (physical
volume). A small 'one-line' patch can fix this, but the lvm2
people are working on other lvm2 stuff. I hope Alasdair Kergon
will be able to get this simple change in LVM2.<br>
<br>
If not, users can manually configure LVM2 to accept bcache
devices as PV by making a small change to their
/etc/lvm/lvm.conf. To build a working initramfs users need to
manually pass the --lvmconf option to dracut, so a kernel
upgrade won't work out-of-the-box.<br>
</tt><span class="bz_comment_user"><span class="vcard redhat_user"><a
class="email" href="mailto:agk@redhat.com" title="Alasdair
Kergon <agk@redhat.com>"><span class="fn"></span></a></span></span><tt><br>
I tested bcache by using a patched LVM2 that accepts bcache as a
PV, hoping the patch will be in F20.<br>
<br>
Anaconda<br>
--------<br>
Currently the team is very busy getting anaconda ready for F20,
and including bcache support may require considerable effort.
Hopefully anaconda has bcache support in F21.<br>
<br>
</tt></div>
<br>
<br>
<tt>More details: <a class="moz-txt-link-freetext" href="https://bugzilla.redhat.com/show_bug.cgi?id=998543">https://bugzilla.redhat.com/show_bug.cgi?id=998543</a>
</tt><tt><br>
</tt><tt><br>
</tt>
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