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Re: [Linux-cluster] AW: GNBD multipath with devicemapper? -- possible solution



On Wed, Apr 20, 2005 at 07:38:19AM +0200, Hansjörg Maurer wrote:
> 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?

I got those numbers on a vanilla 2.6.11 kernel.
Running on a 2.6.9-6.24.EL kernel, I get
45.6608 MB/sec writes 
35.8578 MB/sec reads

Not as pronouced as your numbers, but a noticeable speed difference.

-Ben
> Thank you very much
> 
> Hansjörg
> 
> > 
> >
> > 
> >
> 
> 
> -- 
> _________________________________________________________________
> 
> Dr.  Hansjoerg Maurer           | LAN- & System-Manager
>                                |
> Deutsches Zentrum               | DLR Oberpfaffenhofen
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> __________________________________________________________________
> 
> 
> There are 10 types of people in this world, 
> those who understand binary and those who don't.
> 
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