[Lustre-discuss] replayable IO logging from Lustre's changelog

Rob Stewart robstewart57 at gmail.com
Mon May 20 11:25:35 PDT 2013


Having read the wiki page on Lustre's changelogs [1], I have a
question about one claim "Use changelog entries to exactly replicate
changes in a file system mirror."

Of the record types that the changelog supports, there is not an entry
for WRITE, although one can see when files are created as CREAT is
supported. So whilst the example that page allows me to establish that
a file /mydir/hosts exists from 19:10:37 on 2010.03.24 , I know
nothing about the contents of the file `hosts`.

In order to implement the use case "Use changelog entries to exactly
replicate changes in a file system mirror", you'd need something more
than just the changelog... something that, for example, scp'd from the
IO server the file /mydir/hosts elsewhere. Is there a common procedure
for indeed doing this in Lustre? Or in fact have I missed something in
the wiki page? Are the plans to support WRITE events in Lustre's
changelogs? I'm not sure what that'd look like - you'd probably not
want to overload a changelog with raw binary data. However, having
read "Towards an I/O Tracing Framework Taxonomy" [2], I see that
//Trace [3] does support replayable IO traces. Is replayable IO
logging something that the Lustre community has, or intends on
supporting in the future?

[1] - http://wiki.lustre.org/manual/LustreManual20_HTML/LustreMonitoring.html
[2] - http://www.pdsi-scidac.org/SC07/resources/KONWINSKI-PDSI_Paper-Towards_an_IO_Tracing_Framework_Taxonomy.pdf
[3] - http://www.cs.cmu.edu/~droh/papers/trace-fast07.pdf


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