ZFS doesn't mix well with mmap(2). This is because ZFS uses the ARC
instead of the Solaris page cache. But mmap() uses the latter. So if
anyone maps a file, ZFS has to keep the two caches in sync.
cp(1) uses mmap(2). When you use cp(1) it brings pages of the files it
copies into the Solaris page cache. As long as they remain there ZFS
will be slow for those files, even if you subsequently use read(2) to
access them.
If you reboot, your cpio(1) tests will probably go fast again, until
someone uses mmap(2) on the files again. I think tar(1) uses read(2),
but from my iPod I can't be sure. It would be interesting to see how
tar(1) performs if you run that test before cp(1) on a freshly
rebooted system.
I have done some work with the ZFS team towards a fix, but it is only
currently in OpenSolaris.
The other thing that slows you down is that ZFS only flushes to disk
every 5 seconds if there are no synchronous writes. It would be
interesting to see iostat -xnz 1 while you are running your tests. You
may find the disks are writing very efficiently for one second in
every five.
Hope this helps,
Phil
blogs.sun.com/pgdh
Sent from my iPod
On 4 Jul 2009, at 05:26, Bob Friesenhahn
<bfrie...@simple.dallas.tx.us> wrote:
On Fri, 3 Jul 2009, Bob Friesenhahn wrote:
Copy Method Data Rate
==================================== ==================
cpio -pdum 75 MB/s
cp -r 32 MB/s
tar -cf - . | (cd dest && tar -xf -) 26 MB/s
It seems that the above should be ammended. Running the cpio based
copy again results in zpool iostat only reporting a read bandwidth
of 33 MB/second. The system seems to get slower and slower as it
runs.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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