On Mon, 7 May 2012, Karl Rossing wrote:

On 12-05-07 12:18 PM, Jim Klimov wrote:
During the send you can also monitor "zpool iostat 1" and usual
"iostat -xnz 1" in order to see how busy the disks are and how
many IO requests are issued. The snapshots are likely sent in
the order of block age (TXG number), which for a busy pool may
mean heavy fragmentation and lots of random small IOs..
I have been able to verify that I can get a zfs send at 135MB/sec for a striped pool with 2 internal drives on the same server.

I see that there are a huge number of reads and hardy any reads. Are you SURE that deduplication was not enabled for this pool? This is the sort of behavior that one might expect if deduplication was enabled without enough RAM or L2 read cache.

Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
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