Re: AW: GNBD multipath with devicemapper? -- possible solution

Hi,

thank you for yor reply.

Benjamin Marzinski wrote:

> On Tue, Apr 19, 2005 at 08:37:54AM +0200, Hansjoerg Maurer wrote:
>  
>
> > The most anoying point is for me at the moment the differnence between 
> > gnbd read and write performance.
> > Therefore I am glad, that you as a gnbd-developer answered...
> > In my tests, gnbd write is about two to three times faster the gnbd reads.
> > I tried a lot of things (exporting cached, changing readahead with 
> > blockdev command (on the underlying device), changing TCP-IP buffersizes)
> > but I had nor improvement.
> >
> > In the upper example, I get a write speed of about 85MB/s over gnbd and 
> > a read speed of about 26 MB/s .
> > (the underlying device's sda and sdb manages about 50MB/s (read and write).
> > Therefore read speed is very good....
> >    
>
> Um. On my machines I get 41.6707 MB/sec for reads and 41.6805 MB/sec for
> writes using lmdd, so I don't see your difference.  If I just write to the
> gnbd device, and don't sync the device after the writes I get a write speed of
> 54.3400 MB/sec.  This only takes into account how fast gnbd can write out all
> the requests, not how long it takes for them to actually get written to disk
> on the server. I would be suspicious of a gnbd write speed that is higher than
> the served device's speed.
>
> -Ben 
>  
the device speed of one disk is about 50 MB/s, but the two gnbd's (zwo 
seperate disks) are bundeled to one striped lvm.
Therefore the speed is possible.
I have seen the difference in read and write speed on two installations.
Kernel 2.6.9-6.38.EL and gfs from RHEL4 cvs , tested with cfq and 
anticipatory elevator.
What kernel are you using?

Thank you very much

Hansjörg

>  
>
>  


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Dr.  Hansjoerg Maurer           | LAN- & System-Manager
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