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Hello,
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<BR>
Maybe my input can help you convince. Indeed mounting read only does come in very handy for database logfiles.
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This is the situation:
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A masterdatabase which is online
<BR>
A slavedatabase which is in standby
<BR>
<BR>
In normal operations:
<BR>
------------------------
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The masterdatabase writes duplexed log files and archived log files to the primary drbd device.
<BR>
At night the slavedatabase "wakes up" mounts the secondary drbd device read only and applies the past 24 hours of changes captured in the archived and the online redo log files. When done, the database goes back to standby and the device is umounted.
<BR>
To be more precise, in reality, I mount the device, copy the changes since last night to a local device, unmount, and then work with the local copies. The reason? I don't know how the slavedatabase would react if the online redologfiles changed will rolling forward.
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So far this could also be done with NFS
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<BR>
When a failure happens on the masterdatabase and it goes down:
<BR>
---------------------------------------------------------------------------
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the slavedatabase kicks in (via heartbeat) mounts the drbd device in primary, applies the changes since midnight and fires up in online state.
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This could not be done with NFS because you wouldn't have access anymore. rsync is not an option either because you need the committed changes up to the very last second.
<BR>
<BR>
I think this is a very common setup and drbd is a magnificent tool to reach the goal for this.
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So hope this is convincing enough ;)
<BR>
<BR>
Regards,
<BR>
<BR>
Filip Sergeys
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
On Tue, 2005-03-22 at 17:05, Philipp Reisner wrote:
<BLOCKQUOTE>
<PRE><FONT COLOR="#737373"><FONT SIZE="3"><I>Am Dienstag, 22. März 2005 14:53 schrieb Reine Larsson:</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>> Hi,</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>></FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>> After uplifting from 0.6.12 to 0.7.6 we discover a change in behaviour.</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>> When did this change happen?</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I></FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>from 0.6 -> 0.7</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I></FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>> Is there something that can be done about it?</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I></FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>Well, since users kept on mounting it read only on the secondary</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>and Linux-2.6.x allows us to prohibit read accesses, we decided</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>to do so.</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I></FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I> There are Filesystem out there that may crash the kernel when </FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I> mounted on a self-changing device ;)</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I></FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>Short answer: no</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>Long answer: </FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I> Just convince me that it I want this feature as well,</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I> and it might come back (as runtime configuration)</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I> in 0.7.11.</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I></FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>-Philipp</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I></FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>-- </FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>: Dipl-Ing Philipp Reisner Tel +43-1-8178292-50 :</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>: LINBIT Information Technologies GmbH Fax +43-1-8178292-82 :</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>: Schönbrunnerstr 244, 1120 Vienna, Austria http://www.linbit.com :</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>_______________________________________________</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>drbd-user mailing list</FONT></FONT></I>
<FONT COLOR="#737373"><FONT SIZE="3"><I>drbd-user@lists.linbit.com</FONT></FONT></I></PRE>
</BLOCKQUOTE>
<A HREF="http://lists.linbit.com/mailman/listinfo/drbd-user"><FONT SIZE="3"><I>http://lists.linbit.com/mailman/listinfo/drbd-user</FONT></I></A>
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