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. 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). -- Peter Jeremy Please excuse any delays as the result of my ISP's inability to implement an MTA that is either RFC2821-compliant or matches their claimed behaviour.
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