On Sun, 1 Feb 2009, RW wrote:
***It is recommended that you always use this option when
dumping a snapshot.***
When you dump a snapshot there are, by definition, no changes between
passes. So it's saying that in that case there in no reason not to
cache.
Ah, that makes sense. That being the case, perhaps we can update
the text to:
If dumping from a snapshot, the filesystem is already frozen,
therefore using a cache with a snapshot will ensure that
consistency is maintained while also providing best performance.
If that sounds good, I'll make a doc patch.
Out of curiosity, under what circumstances is the improved performance
the most likely? I dump from cron when the system usage is low, and
haven't noticed any significant difference in time with or without
cacheing -- but I haven't done any testing under heavy load, nor with
limited RAM, so there are many mbufs available in any case.
Thanks for the info,
Andrew.
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