On Wed, 2005-07-13 at 22:18 +0100, David Greaves wrote: > Ming Zhang wrote: > > >>component partitions, e.g. /dev/sda7: 39MB/s > >>raid device /dev/md2: 31MB/s > >>lvm device /dev/main/media: 53MB/s > >> > >>(oldish system - but note that lvm device is *much* faster) > >> > >> > > > >this is so interesting to see! seems that some read ahead parameters > >have negative impact. > > > > > I guess each raw device does some readahead, then the md0 does some > readahead and then the lvm does some readahead. Theoretically the md0 > and lvm should overlap - but I guess that much of the raw device level > readahead is discarded. > > David > for a streaming read, what you readahead now will always be used exact once in near future. at least i think raw device readahead can be turned on at the same time with one of OS components, raid or lvm, readahead being turned on. but in your case, u get best result when turn only one on.
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