[olug] Slow read speeds-SuSE

[Craig Wolf]

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 >>>
Craig,

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.

DanL

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