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List:       dragonfly-commits
Subject:    Re: cvs commit: src/sbin/hammer cmd_mirror.c cmd_pseudofs.c hammer.8
From:       Michael Neumann <mneumann () ntecs ! de>
Date:       2008-07-31 7:25:03
Message-ID: 489168CF.9090600 () ntecs ! de
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Matthew Dillon wrote:
> :  Log:
> :  HAMMER Utilities: Streaming mirroring!
> :  
> :  * Add a new streaming mirroring feature called 'mirror-stream' which works
> 
>     Please note that this is not quite ready for testing yet.  There is
>     a race between normal filesystem writes and the mirror's B-Tree scan
>     which can cause a DATA CRC and other assertions.
> 
>     In fact, the only known bugs in the filesystem at the moment, assuming
>     I fixed that blocking bug reported on the lists, is due to buffer
>     cache aliasing between vnode-mapped buffers and device-mapped buffers.
>     I think the cluster_read I do on the device-mapped buffers is causing
>     the headache.
> 
>     I hope to have the bug fixed by tomorrow evening.
> 
>     The new bandwidth-limited streaming mirroring feature is going to be
>     very spiffy!   It's working except for the above bug!
> 
>     It will make it possible to have a streaming mirror continuously
>     running in the background but not eating much in the way of system
>     resources.  So instead of batching your backups you would be able to
>     maintain a continuously running backup.  It should also work well for
>     sporatically connected boxes, like a laptop, where you want it to
>     maintain a backup automatically whenever it happens to have internet
>     connectivity, but also not eat up too much of your WIFI bandwidth.

That's pretty cool! One question though: If I'd like to have the exact
same snapshots on each machine, is that as easy as just "copying" the
softlinks? That is, are the transaction ids (those @@0x... numbers :)
identical on the master and it's mirrors?

Regards,

   Michael
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