[Xen-users] Re: [rhelv5-list] shared storage manual remount ...

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Mon, Feb 08, 2010 at 04:46:59PM +0100, Zoran Popovi? wrote:
>    Tell me what would you like to know more about my environment - I was
>    trying to give all relevant information, at least concerning this issue.
>    And, btw,  echo 1 > /proc/sys/vm/drop_caches  does the  work I have needed
>    - if I do this I get results I need (and, for example, if I don't do that
>    after snapshot restore on the storage, my HVM Windows guest usually start
>    chkdsk during boot).

So you're saying you need drop_caches *with* phy for the other host to see the 
disk contents? 

-- Pasi

>    ZP.
> 
>    2010/2/8 Zavodsky, Daniel (GE Capital) <[1]daniel.zavodsky@xxxxxx>
> 
>      Hello,
>          I have tried this and it works here... caching is not used for phy:
>      devices, only buffering but it is flushed frequently so it is not a
>      problem. Maybe you should post some more info about your setup?
> 
>      Regards,
>          Daniel
> 
>    --------------------------------------------------------------------------
> 
>      From: [2]rhelv5-list-bounces@xxxxxxxxxx
>      [mailto:[3]rhelv5-list-bounces@xxxxxxxxxx] On Behalf Of Zoran Popoviæ
>      Sent: Thursday, February 04, 2010 1:40 AM
>      To: Red Hat Enterprise Linux 5 (Tikanga) discussion mailing-list;
>      [4]xen-users@xxxxxxxxxxxxxxxxxxx
>      Subject: [rhelv5-list] shared storage manual remount ...
>      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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