nfs slowdown (RELENG_8)

[Mike Tancsa]

On 6/24/2014 10:14 AM, Mike Tancsa wrote:
>
> I also just tried with an igb nic and the same issue.  These are i386
> boxes. I wonder if its something to do with that. (non PAE kernel)
>


OK, its not related to i386 as I found another box with em nics, i386 
that works at full speed.  One more strange issue I discovered is that 
there is a difference between dd and cat on the problem boxes. 
Normally, this would be uninteresting to me other than the fact that it 
seems the same underlying issue is impacting the performance of dump 
over NFS.

e.g. on the two problem client problem boxes, if I do a simple test like

# dd if=/dev/zero of=/nfsbackup/test count=200000 bs=1024
200000+0 records in
200000+0 records out
204800000 bytes transferred in 1.767594 secs (115863704 bytes/sec)

which is close to gigabit speeds-- all is good.

and if I do

# cat /dev/zero | dd of=/nfsbackup/test count=200000 bs=1024
200000+0 records in
200000+0 records out
204800000 bytes transferred in 1.771045 secs (115637945 bytes/sec)

Also, close to gigabit speeds... All is still good.

But if I do
# cat /dev/zero > /nfsbackup/test

Its down to 25Mb/s

Now, if this were consistent across all my boxes, I would not be too 
interested.

Why is cat with a redirect so much slower, and why slower just on some 
boxes and not others ?!?!

	---Mike

-- 
-------------------
Mike Tancsa, tel +1 519 651 3400
Sentex Communications, mike at sentex.net
Providing Internet services since 1994 www.sentex.net
Cambridge, Ontario Canada   http://www.tancsa.com/