Re: default mount options

[L A Walsh <xfs@tlinx.org>]

Dave Chinner wrote:
> For /some/ RAID controllers in /some/ modes. For example, the
> megaraid driver that has been ignoring cache flushes for over 9
> years because in RAID mode it doesn't need it. However, in JBOD
> mode, that same controller requires cache flushes to be sent because
> it turns off sane cache management behaviour in JBOD mode...
---
  Lovely. For better or worse, none of my HW-based LSI-raid cards have
been able to do JBOD.
do JBOD.  

> This is a clear example of why "barriers" should always be on and
> cache flushes always passed through to the storage - because we just
> don't know WTF the storage is actually doing with it's caches.
----
	When it comes to JBOD, its not so clear about where caching
helps the most.  

	Related -- wondering about how external journals would 
affect need for barriers.  Haven't thought about it much, but it seems
like one would get alot of bang-for-the-buck to put journals on
SSD's.  _If_ data written to SSD's becomes "safe" as soon as it is 
accepted by SSDs (not saying it *is*, but _if_ it is), then how
"needed" is ordering of writes for rotating media -- apart from
special use/need cases like apps maintaining their own data-integrity
journals like DB's or such?  Just wondering about how increasing use
of SSD's might affect the need for barriers.

	Anyway, I have the illusion that I am mostly clear about
current params (at least until my next disillusioning)...   ;-)

-l