Hi,
thank you for yor reply.
Benjamin Marzinski wrote:
On Tue, Apr 19, 2005 at 08:37:54AM +0200, Hansjoerg Maurer wrote: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.
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
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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