In message: <[email protected]> Peter Jeremy <[email protected]> writes: : On 2009-Jan-09 09:50:27 -0700, "M. Warner Losh" <[email protected]> wrote: : >The read kBps was 3x the write kBps. : ... : >Any ideas what gives? I observed this with 16MB cache and with 32MB : >cache, fwiw. : : I've seen this as well. AFAIK, this is a side-effect of dump's caching. : : My top-of-head explanation is that each dump process has its own cache : but actual I/O is round-robined on a (roughly) block scale so a large : contiguous file will wind up in each 'slave' process's cache. : : The most obvious (and easiest) fixes are to either implement a shared : cache (though this means another level of inter-process communication) : or only use a single 'slave' process when caching is enabled.
I'll have to look into this... Most of the files I was backing up were large contiguous files (26 10GiB .dv files from my camera). : The cache algorithm could probably be enhanced as well - apart from : inode blocks, any block will only be accessed once so once a block has : been accessed, it can be purged from the cache (which is completely : opposite to a "normal" cache). Yes, read everything, purge once it is touched. Warner _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[email protected]"
