[olug] Slow read speeds-SuSE

Craig Wolf cjwolf at mpsomaha.org
Thu Apr 29 14:37:12 UTC 2010

Output from free -m: 

mil-sac:~ # free -m 
             total       used       free     shared    buffers     cached 
Mem:          3946       3379        567          0          2       1766 
-/+ buffers/cache:       1610       2336 
Swap:         2055          0       2055 

Don't think that is the issue but will have to look at this during a backup as well.

Craig Wolf
Linux Server Support
Backups Administrator
Desktop/Network Specialist
Desk: (402)715-6283
Cell: (402)510-0301

>>> Dan Linder <dan at linder.org> 4/29/2010 9:07 AM >>>

You wrote:

> Ok, my backups from one of my linux servers takes 5 days to finish...my
> window is 36 hours, not working right.  Throughput of about 1.5GB/hour.
> So in my testing, copying a 158MB directory to the server takes about 1
> Minute 5 seconds.  Copying same structure off the box takes almost 7
> minutes.  Network switches show no issues/error.  iostat shows slow to no
> throughput at all on read.

I've been working on a performance issue on a customers Linux box.  His is a
production box but I could re-create the problem exactly by using up the RAM
so the OS couldn't cache well.  We could see a big difference if we rebooted
the box, ran a test once to cache the data, then re-ran the test a few more
times.  The results were staggering to say the least: 7+ minutes to less
than 10 seconds in my case.

Thankfully in my situation I am able to re-work some code so the OS cache
effect can be mitigated.

If you run "free -m", the "-/+ buffers/cache" will show how much RAM the OS
is using to cache file objects.  If this is close to zero, common disk
accesses may be slowing down all disk IO too.


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