WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] double or triple access to ext2, ext3 or other partition

To: Luke Kenneth Casson Leighton <lkcl@xxxxxxxx>
Subject: Re: [Xen-devel] double or triple access to ext2, ext3 or other partitions
From: Mark Williamson <maw48@xxxxxxxxxxxxxxxx>
Date: Tue, 23 Nov 2004 17:30:04 +0000 (GMT)
Cc: xen-devel@xxxxxxxxxxxx
Delivery-date: Tue, 23 Nov 2004 17:31:30 +0000
Envelope-to: xen+James.Bulpin@xxxxxxxxxxxx
In-reply-to: <20041123171312.GC6250@xxxxxxxx>
List-archive: <http://sourceforge.net/mailarchive/forum.php?forum=xen-devel>
List-help: <mailto:xen-devel-request@lists.sourceforge.net?subject=help>
List-id: List for Xen developers <xen-devel.lists.sourceforge.net>
List-post: <mailto:xen-devel@lists.sourceforge.net>
List-subscribe: <https://lists.sourceforge.net/lists/listinfo/xen-devel>, <mailto:xen-devel-request@lists.sourceforge.net?subject=subscribe>
List-unsubscribe: <https://lists.sourceforge.net/lists/listinfo/xen-devel>, <mailto:xen-devel-request@lists.sourceforge.net?subject=unsubscribe>
References: <20041123171312.GC6250@xxxxxxxx>
Sender: xen-devel-admin@xxxxxxxxxxxxxxxxxxxxx
2) at every point in the ext2 and ext3 filesystem drivers where
SMP-driven locking is performed, add in xen-semaphore usage and locking
(as well / instead).

It's not quite that simple: the ext driver in each domain will be caching data related to its filesystem changes in memory. In an SMP system, both CPUs can see this cached data in memory, whereas separate virtual machines cannot see what each other are caching.

Mounting the same partition is already possible using a cluster filesystem (like GFS). Cluster filesystems handle the extra locking correctly because they're designed for use with multiple hosts sharing a disk (e.g. over a SAN). They'll even work with multiple writers.

It is also possible to export any filesystem via NFS and have it mounted by multiple domains or to have copy-on-write semantics (e.g. using LVM) so that domains never see each others changes (thus circumventing the problem).

HTH,
Mark


--
--
<a href="http://lkcl.net";>http://lkcl.net</a>
--


-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://productguide.itmanagersjournal.com/
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/xen-devel



-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/xen-devel

<Prev in Thread] Current Thread [Next in Thread>