Hello,

On 08/20/2010 05:18 PM, Ric Wheeler wrote:

On 08/20/2010 09:22 AM, Christoph Hellwig wrote:

quoted

FYI: here's a little writeup to document the new cache flushing scheme,
intended to replace Documentation/block/barriers.txt.  Any good
suggestion for a filename in the kernel tree?

I was thinking that we might be better off using the "durable
writes" term more since it is well documented (at least in the
database world, where it is the "D" in ACID properties).  Maybe
"durable_writes_support.txt" ?

The term is very foreign to people outside of enterprise / database
loop.  writeback-cache.txt or write-cache-control.txt sounds good
enough to me.

quoted

The Linux block layer provides a two simple mechanism that lets filesystems
control the caching behavior of the storage device.  These mechanisms are
a forced cache flush, and the Force Unit Access (FUA) flag for requests.

Should we mention that users can also disable the write cache on the
target device?

It might also be worth mentioning that storage needs to be properly
configured - i.e., an internal hardware RAID card with battery
backing needs can expose itself as a writethrough cache *only if* it
actually has control over all of the backend disks and can
flush/disable their write caches.

It might be useful to give several example configurations with
different cache configurations.  I don't have much experience with
battery backed arrays but aren't they suppose to report write through
cache automatically?

Thanks.

-- 
tejun