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Re: RES: [Xen-users] Shared volume: Software-ISCSI or GFS or OCFS2?

To: Bruno Bertechini <bruno.bertechini@xxxxxxxxxxx>
Subject: Re: RES: [Xen-users] Shared volume: Software-ISCSI or GFS or OCFS2?
From: John Haxby <john.haxby@xxxxxxxxxx>
Date: Wed, 19 Nov 2008 13:29:35 +0000
Cc: "'Rustedt, Florian'" <Florian.Rustedt@xxxxxxxxxxx>, 'Bastian Blank' <bastian@xxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
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Bruno Bertechini wrote:
Can someone explain why we should use NFS? It is fairly slow and unsecure.

It depends. If you're using a NetApp server or an EMC Celerra then NFS isn't slow and it's secure "enough". The big advantage of NFS is that it is easy to get working and it's well understood by a lot of people.

Why not use some clustered FS ?
NFS is a clustered file system -- it's a file system that's visible across a cluster. If you mean an HA cluster, then yes, you can use something like ocfs2 or gfs/gfs2. These things, however, are designed when you want concurrent access to individual files within the file system and for Xen disk image files you don't normally want that -- unless you're using a clustered file system in the guests of course.

The right file system for you depends, in detail, what you want to do.

Are there alternatives ?

For Xen virtual disk files there are several alternatives: iSCSI and nbd both provide access to logical devices across a standard network. That EMC Celerra I mentioned supports iSCSI as well as NFS and, depending on what you're doing, you may prefer that. If you have a fibrechannel SAN or even infiniband you can use those as well.

For my non-production purposes I use NFS because it's easy and fast (that is, the quickest way to get data between two machines over the gigabit LAN is using NFS). If I were setting up a production cluster then I would start with some shared non-local storage and I'd probably be looking at NFS again or iSCSI and the choice then depends on what the disk array box supports and is good at. For a system built entirely out of stock PCs, well, I wouldn't. I wouldn't build a production cluster of any size that way: I want proper storage.

What you do depends on what you're planning to use these machines for and how much time and money you're spending.


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