cvs commit: src/sbin/hammer cmd_mirror.c cmd_pseudofs.c hammer.8 hammer.c hammer.h

[Matthew Dillon]

:  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.

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>