[Linux-cluster] AW: GNBD multipath with devicemapper? -- possible solution
Hansjörg Maurer
Hansjoerg.Maurer at dlr.de
Wed Apr 20 05:38:19 UTC 2005
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
>
>
>
>
--
_________________________________________________________________
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 at dlr.de
Fax: 08153/28-1134 | WWW: http://www.robotic.dlr.de/
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