On Sat, Oct 20, 2012 at 7:39 AM, Edward Ned Harvey (opensolarisisdeadlongliveopensolaris) < opensolarisisdeadlongliveopensola...@nedharvey.com> wrote:
> > From: Timothy Coalson [mailto:tsc...@mst.edu] > > Sent: Friday, October 19, 2012 9:43 PM > > > > A shot in the dark here, but perhaps one of the disks involved is taking > a long > > time to return from reads, but is returning eventually, so ZFS doesn't > notice > > the problem? Watching 'iostat -x' for busy time while a VM is hung > might tell > > you something. > > Oh yeah - this is also bizarre. I watched "zpool iostat" for a while. It > was showing me : > Operations (read and write) consistently 0 > Bandwidth (read and write) consistently non-zero, but something small, > like 1k-20k or so. > > Maybe that is normal to someone who uses zpool iostat more often than I > do. But to me, zero operations resulting in non-zero bandwidth defies > logic. > > It might be operations per second, and is rounding down (I know this happens in DTrace normalization, not sure about zpool/zfs), try an interval of 1 (perhaps with -v) and see if you still get 0 operations. I haven't seen zero operations with nonzero bandwidth on my pools, I always see lots of operations in bursts, so it sounds like you might be on to something. Also, iostat -x shows device busy time, which is usually higher on the slowest disk when there is an imbalance, while zpool iostat does not. So, if it happens to be a single device's fault, iostat -nx has a better chance of finding it (the n flag translates the disk names to the device names used by the system, so you can figure out which one is the problem). Tim
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