Re: [dm-devel] Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md.

Valdis.Kletnieks@vt.edu wrote:

On Tue, 10 Jul 2007 14:39:41 EDT, Ric Wheeler said:

quoted

All of the high end arrays have non-volatile cache (read, on power loss, it is a 
promise that it will get all of your data out to permanent storage). You don't 
need to ask this kind of array to drain the cache. In fact, it might just ignore 
you if you send it that kind of request ;-)

OK, I'll bite - how does the kernel know whether the other end of that
fiberchannel cable is attached to a DMX-3 or to some no-name product that
may not have the same assurances?  Is there a "I'm a high-end array" bit
in the sense data that I'm unaware of?

Well, the array just has to tell the kernel that it doesn't to write
back caching.  The kernel automatically selects ORDERED_DRAIN in such case.

-- 
tejun