On Tue, 17 Jul 2012, Andrew Hume wrote:
i have two linux servers each of which has the same piece of SAN attache dto it as a LUN. that is, svra:/dev/sdbd is the same volume (or more exactly WWN) as svrb:/dev/sdaf.what i want to do is write something on svra to /dev/sdbd and then be able to read it on svrb from /dev/sdaf. in principle this should work, but on Linux the buffer cache always inserts doubt. how do i reliably probe /dev/sdaf for new content? there is no filesystem involved; i am just talking about raw disk blocks.
you also need to worry about possible buffers in your SAN I/O cards. opening it O_DIRECT may work to bypass the caches in linux, but you are getting into tricky areas here. I'd suggest trying O_DIRECT, but you may need to ask some kernel experts if this is enough.
David Lang
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