On Thu, Jul 23, 2015 at 06:49:55PM -0600, Theo de Raadt wrote:
> > There was a great discussion about softdep recently:
> >
> > https://marc.info/?t=142164016900001&r=1&w=2
> >
> > It needs extra memory, so the FAQ warns against its use on really
> > old architectures.
> >
> > tedu@ described the two main deterrents:
> >
> > https://marc.info/?l=openbsd-misc&m=142294185000751&w=2
> >
> > Might it be worth making default for AMD64? The performance gain is
> > big in many cases.
> >
> There is no way this diff is going in.
>
> When softdep is 100% reliable, then we can talk.
> Enabling it prematurely is ridiculous. Considering the defects
> are clearly described as lockups, disk space corruption -- with
> such a suggestion I must ask --who's side are you on??
The first issue that Ted mentions is just characteristic of soft
updates, right? He discusses it more here:
https://marc.info/?l=openbsd-misc&m=142250784228719&w=2
The second one sounds specific to implementation bugs. I didn't know how
well those had been combed out.
Here's another diff. Someone who knows more than I do about soft updates
can probably word it better.
Index: faq/faq14.html
===================================================================
RCS file: /cvs/www/faq/faq14.html,v
retrieving revision 1.253
diff -u -p -r1.253 faq14.html
--- faq/faq14.html 2 Jul 2015 05:49:04 -0000 1.253
+++ faq/faq14.html 24 Jul 2015 01:25:03 -0000
@@ -913,6 +913,12 @@ with soft updates.
</pre></blockquote>
<p>
+While soft updates are widely used and generally reliable, they can worsen the
+impact of I/O errors. Also, if many small files are quickly modified on a slow
+disk, the fileystem may struggle to cope with the accumulating deferred
+updates.
+
+<p>
Note to sparc users: Do not enable soft updates on sun4 or sun4c
machines. These architectures support only a very limited amount of
kernel memory and cannot use this feature. However, sun4m machines are
Index: faq/obsd-faq.txt
===================================================================
RCS file: /cvs/www/faq/obsd-faq.txt,v
retrieving revision 1.39
diff -u -p -r1.39 obsd-faq.txt
--- faq/obsd-faq.txt 5 Jun 2015 12:04:13 -0000 1.39
+++ faq/obsd-faq.txt 24 Jul 2015 01:25:04 -0000
@@ -11531,6 +11531,11 @@ that has one partition sd0a that we wish
/dev/sd0a / ffs rw,softdep 1 1
+While soft updates are widely used and generally reliable, they can worsen the
+impact of I/O errors. Also, if many small files are quickly modified on a slow
+disk, the fileystem may struggle to cope with the accumulating deferred
+updates.
+
Note to sparc users: Do not enable soft updates on sun4 or sun4c machines.
These architectures support only a very limited amount of kernel memory and
cannot use this feature. However, sun4m machines are fine.
