[DRBD-user] benchmark / setup Questions

01flipstar at web.de 01flipstar at web.de
Fri Jun 22 12:13:06 CEST 2007

Note: "permalinks" may not be as permanent as we would like,
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Hi List,

im new in drbd and ha-linux but in the last days i have spend quite some
time with my little setup.

Setup 2 PC's each: 
~ 512 MB/Ram

Suse 10.2

What I want is a OCFS2 partition on top of a drbd (activ/activ) setup.

Everything works so fare but it was quite hard to find out that:

- in a activ/activ setup only protocoll C is supported -> found in the
sourcecode only (call me optimist)

The problem is that when both pc's concurrently write to one file the
performance gets really bad.

My benchmark writes single lines with write() into a file, for one
minute the overall throughput is ok but for some lines it takes
about 300-500msec.

I created two kernel one with preemption and timefreq=1000 and one
without preemption and timefreq=100 but the times did not vary.

Maybe the DLM is the bottleneck??

I thought that I could improve the performance by not writing
the mata-data to the disk but to a ramdisk -> yes for tesing only :-)

because the meta-data gets updated by very change on the disk right??
so the disk-head has to be moved and can not write sequential???

So I tryed to add 

    meta-disk /dev/ram0[0];

to my /etc/drbd.conf.
When I create the meta-data I get:

    Command 'drbdmeta /dev/drbd0 v08 /dev/ram0 0 write-dev-uuid
587CBE437E1F2D14' terminated with exit code 255

The Ramdisk is > 128MB so this should not be the problem.

Is there a way to get the meta-data on a ramdisk?
Has somebody experiences with ocfs2 and drbd and can give me a hint
what to change??

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