What version of Solaris / OpenSolaris are you using? Older versions use
mmap(2) for reads in cp(1). Sadly, mmap(2) does not jive well with ZFS.
To be sure, you could check how your cp(1) is implemented using truss(1)
(i.e. does it do mmap/write or read/write?)
<aside>
I find it interesting that ZFS's mmap(2) deficiencies are now dictating
implementation of utilities which may benefit from mmap(2) on other
filesystems. And whilst some might argue that mmap(2) is dead for file
I/O, I think it's interesting to note that Linux appears to have a
relatively efficient mmap(2) implementation. Sadly, this means that some
commercial apps which are mmap(2) heavy currently perform much bettter
on Linux than Solaris, especially ZFS. However, I doubt that Linux uses
mmap(2) for reads in cp(1).
</aside>
You could also try using dd(1) instead of cp(1).
However, it seems to me that you are using bs=1G count=8 as a lazy way
to generate 8GB (because you don't want to do the math on smaller
blocksizes?)
Did you know that you are asking dd(1) to do 1GB read(2) and write(2)
systems calls using a 1GB buffer? This will cause further pressure on
the memory system.
In performance terms, you'll probably find that block sizes beyond 128K
add little benefit. So I'd suggest something like:
dd if=/dev/urandom of=largefile.txt bs=128k count=65536
dd if=largefile.txt of=./test/1.txt bs=128k &
dd if=largefile.txt of=./test/2.txt bs=128k &
Phil
http://harmanholistix.com
bank kus wrote:
dd if=/dev/urandom of=largefile.txt bs=1G count=8
cp largefile.txt ./test/1.txt &
cp largefile.txt ./test/2.txt &
Thats it now the system is totally unusable after launching the two 8G copies. Until these copies finish no other application is able to launch completely. Checking prstat shows them to be in the sleep state.
Question:
<> I m guessing this because ZFS doesnt use CFQ and that one process is allowed
to queue up all its I/O reads ahead of other processes?
<> Is there a concept of priority among I/O reads? I only ask because if root
were to launch some GUI application they dont start up until both copies are done. So
there is no concept of priority? Needless to say this does not exist on Linux 2.60...
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