[OpenAFS] Read-Write Disconnected Mode - How does it work?

[William McCabe]

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Simon,

Thanks for the information. To operate on the files while the volume is disconnected, do you need to have the server software installed, or do all of these commands work with the client?

Thanks,

Bill

--- On Sat, 1/31/09, Simon Wilkinson <sxw@inf.ed.ac.uk> wrote:
From: Simon Wilkinson <sxw@inf.ed.ac.uk>
Subject: Re: [OpenAFS] Read-Write Disconnected Mode - How does it work?
To: wlm020279@yahoo.com
Cc: openafs-info@openafs.org
Date: Saturday, January 31, 2009, 6:55 PM

On 31 Jan 2009, at 23:34, William McCabe wrote:

> The latest version of openafs 1.5.57 can use volumes in a disconnected
read-write mode.

Indeed it can. The work was done by Dragos Tatulea as part of last year's
Google Summer of Code.

> Where can I find some documentation for how to use this feature? Is the
feature stable? What are the bugs?

There's not much user documentation available. Disconnected operations is
still under active development - whilst I'd love to get feedback from power
users who are testing it, it probably isn't entirely ready for production
use. The major showstopper here is that we don't have a mechanism for
preserving the state of the cache across machine reboots. This means that if you
reboot your machine for any reason whilst disconnected, you lose all of the
changes made whilst in the disconnected state. Obviously, this is a significant
data loss issue and one that needs to be resolved before its ready for
widespread use.

That said, of the currently known bugs in disconnected, which are tracked in RT
at 
http://rt.central.org/rt/Ticket/Display.htmlid=124148&user=guest&pass=guest
there don't appear to be any other significant data loss issues, and I'd
be very grateful to hardy souls who wish to try it out and provide additional
bug reports.

The user interface is currently pretty primitive (the other major issue that we
need to resolve before it's 'done').

Before disconnecting, you must first prime your cache with all of the files you
wish to use whilst disconnected. Eventually, we will have a pinning mechanism
which will allow the cache manager to do this for you. I typically prime my
cache by doing something along the lines of
find . | xargs cat > /dev/null

Then, you can take the cache manager disconnected by running (as root)
fs discon offline

You may then read and write files in the primed set as you see fit.

When you are back on a decent network connection, you can go back online by
running, as root, and
with appropriate tokens:
fs discon online

This may fail either due to conflicts on the server, or due to transient errors
such as connection timeouts. If it does so, you can retry simply by running the
command again. Server conflicts currently have to be repaired by hand. If
you're in a situation where you just can't fix the problem, and
you're happy to discard the data, 'fs discon online -force' will
reconnect you, throwing away any stored changes.

I've so far run a number of file system test utilities against disconnected
mode, as well as using it for some day to day work, and a large number of
package builds. I'm not currently aware of any way to break the current
code. There are some additional fixes in CVS, over the 1.5.57 release, so if you
are interested in testing, using the tip of the 1.5 branch is a good place to
start.

If you do try it out, please do let me know how you get on!

Thanks,

Simon.


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<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;"><br>Simon,<br><br>Thanks for the information. To operate on the files while the volume is disconnected, do you need to have the server software installed, or do all of these commands work with the client?<br><br>Thanks,<br><br>Bill<br><br>--- On <b>Sat, 1/31/09, Simon Wilkinson <i>&lt;sxw@inf.ed.ac.uk&gt;</i></b> wrote:<br><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;">From: Simon Wilkinson &lt;sxw@inf.ed.ac.uk&gt;<br>Subject: Re: [OpenAFS] Read-Write Disconnected Mode - How does it work?<br>To: wlm020279@yahoo.com<br>Cc: openafs-info@openafs.org<br>Date: Saturday, January 31, 2009, 6:55 PM<br><br><pre>On 31 Jan 2009, at 23:34, William McCabe wrote:<br><br>&gt; The latest version of openafs 1.5.57 can use volumes in a disconnected<br>read-write mode.<br><br>Indeed it can. The work was done by Dragos Tatulea as
 part of last year's<br>Google Summer of Code.<br><br>&gt; Where can I find some documentation for how to use this feature? Is the<br>feature stable? What are the bugs?<br><br>There's not much user documentation available. Disconnected operations is<br>still under active development - whilst I'd love to get feedback from power<br>users who are testing it, it probably isn't entirely ready for production<br>use. The major showstopper here is that we don't have a mechanism for<br>preserving the state of the cache across machine reboots. This means that if you<br>reboot your machine for any reason whilst disconnected, you lose all of the<br>changes made whilst in the disconnected state. Obviously, this is a significant<br>data loss issue and one that needs to be resolved before its ready for<br>widespread use.<br><br>That said, of the currently known bugs in disconnected, which are tracked in RT<br>at
 <br>http://rt.central.org/rt/Ticket/Display.htmlid=124148&amp;user=guest&amp;pass=guest<br>there don't appear to be any other significant data loss issues, and I'd<br>be very grateful to hardy souls who wish to try it out and provide additional<br>bug reports.<br><br>The user interface is currently pretty primitive (the other major issue that we<br>need to resolve before it's 'done').<br><br>Before disconnecting, you must first prime your cache with all of the files you<br>wish to use whilst disconnected. Eventually, we will have a pinning mechanism<br>which will allow the cache manager to do this for you. I typically prime my<br>cache by doing something along the lines of<br>find . | xargs cat &gt; /dev/null<br><br>Then, you can take the cache manager disconnected by running (as root)<br>fs discon offline<br><br>You may then read and write files in the primed set as you see fit.<br><br>When you are back on a decent network connection, you can go back
 online by<br>running, as root, and<br>with appropriate tokens:<br>fs discon online<br><br>This may fail either due to conflicts on the server, or due to transient errors<br>such as connection timeouts. If it does so, you can retry simply by running the<br>command again. Server conflicts currently have to be repaired by hand. If<br>you're in a situation where you just can't fix the problem, and<br>you're happy to discard the data, 'fs discon online -force' will<br>reconnect you, throwing away any stored changes.<br><br>I've so far run a number of file system test utilities against disconnected<br>mode, as well as using it for some day to day work, and a large number of<br>package builds. I'm not currently aware of any way to break the current<br>code. There are some additional fixes in CVS, over the 1.5.57 release, so if you<br>are interested in testing, using the tip of the 1.5 branch is a good place to<br>start.<br><br>If you do try it out, please do
 let me know how you get on!<br><br>Thanks,<br><br>Simon.<br><br></pre></blockquote></td></tr></table>
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