I am wondering if there is a way to solve the following problem: I suppose that the usual way is to establish distributed file system with locking mechanisms like it is possible with GFS and Red Hat Cluster Suite or similar, but I am interested in doing some of this manually and ONLY with raw devices (no file system), or simply in knowing some general principles. The case: I have a VLUN (on FC SAN) presented on two servers, but mounted only on one host - to be more precise, used by a Xen HVM guest system as a raw physical phy:// drive. Then, I put this guest down, and bring it manually up on second host - it can see changed images, and make changes to the presented disks. Then I put it down there, and bring it up again on the first host - BUT THEN, this guest (or host) doesn't see changes made by the second system, it still sees the picture as it was the way it left it. Or even better, if I bring HVM guest on a host, then put it down, make restore of his disks on the storage (I am using HP EVA8400, restoring original disk from a snapshot - it does have redundant controllers but their cache must be in sync for sure), and then bring it up - it still sees things on the disks as they were before restore. But if I _RESTART_ the host, it can see restored disks correctly. Now, I am wondering why is this happening, and if it is possible somehow to resync with the storage without restart (I wouldn't like that on production ! and on our windows systems this is possible) ... I've tried sync (but that is like flushing buffer cache), and I didn't try echo 3 > /proc/sys/vm/drop_caches after that (I've just come upon some articles about that), and I am not sure if that would really invalidate cache and help me. What is the right way of dong this ? Please, help ... ZP.
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