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 > f. Luft- und Raumfahrt e.V. | > Institut f. Robotik | > Postfach 1116 | Muenchner Strasse 20 > 82230 Wessling | 82234 Wessling > Germany | > | > Tel: 08153/28-2431 | E-mail: Hansjoerg.Maurer@xxxxxx > Fax: 08153/28-1134 | WWW: http://www.robotic.dlr.de/ > __________________________________________________________________ > > > There are 10 types of people in this world, > those who understand binary and those who don't. > > -- > > Linux-cluster@xxxxxxxxxx > http://www.redhat.com/mailman/listinfo/linux-cluster -- Linux-cluster@xxxxxxxxxx http://www.redhat.com/mailman/listinfo/linux-cluster
