Messages in this thread | | | Subject | Re: *Really* bad I/O latency with md raid5+dm-crypt+lvm | From | Mike Galbraith <> | Date | Mon, 12 Oct 2009 19:37:56 +0200 |
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On Mon, 2009-10-12 at 16:48 +0200, Tomasz Chmielewski wrote: > > Summary: I was hoping to use a layered storage setup, namely lvm on > > dm-crypt on md raid5 for a new box I'm setting up, but that isn't > > looking so good since a single heavyish writer will monopolise any and > > all I/O on the "device". F. ex. while cp'ing a few GB of data from an > > external disk to the array it takes ~10sec to run ls and ~2min to > > start aptitude. Clueless attempts at a diagnosis below. > > Did you try running strace to see where ls pauses? > > Did you try running latencytop (and generally, top/htop while doing your > tests)? > > > (...) > > > Anyway, as soon as I copy something to the array or create a larger > > (upwards of a few hundred MiB) tar archive the box becomes utterly > > unresponsive until that job is finished. Even on the local console the > > completion time for a simple ls or cat is of the order of tens of > > seconds, just forget about launching emacs. > > Now I know that people have been ranting about desktop responsiveness > > for a while but that was very much an abstract thing for me until now. > > I think the above (big latency when doing some bigger IO) is a general > Linux problem.
It would be interesting to test latest -rc. Though it may prove to be unrelated. the symptoms sound very much like a recent thread wrt writers starving readers.
-Mike
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