On Fri, Jun 28, 2013 at 11:34:18AM -0400, Josef Bacik wrote: > On Fri, Jun 28, 2013 at 02:59:45PM +0100, Martin wrote: > > On kernel 3.8.13: > > > > Using two equal performance SATAII HDDs, formatted for btrfs raid1 for > > both data and metadata and: > > > > The second disk appears to suffer about x8 the read activity of the > > first disk. This causes the second disk to quickly get maxed out whilst > > the first disk remains almost idle. > > > > Total writes to the two disks is equal. > > > > This is noticeable for example when running "emerge --sync" or running > > compiles on Gentoo. > > > > > > Is this a known feature/problem or worth looking/checking further? > > So we balance based on pids, so if you have one process that's doing a lot of > work it will tend to be stuck on one disk, which is why you are seeing that > kind > of imbalance. Thanks,
The other scenario is if the sequence of processes executed to do each compilation step happens to be an even number, then the heavy-duty file-reading parts will always hit the same parity of PID number. If each tool has, say, a small wrapper around it, then the wrappers will all run as (say) odd PIDs, and the tools themselves will run as even pids... Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- Startle, startle, little twink. How I wonder what you think. ---
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