[DRBD-user] DRBD fsync() seems to return before writing to disk

Shaun Thomas sthomas at optionshouse.com
Wed Jun 20 19:43:16 CEST 2012

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


On 06/20/2012 11:51 AM, Phil Frost wrote:

> Just to check my sanity further, I just did a test of a DRBD device
> directly on a partition of a SATA drive. No LVM, no MD; just a plain
> SATA drive and DRBD. I reached the same conclusion, DRBD is not
> observing fsync(), O_SYNC, etc., and it's not for lack of support on
> the underlying device. Can anyone reproduce?

Interesting. I don't have time to test that right now, but now I'm 
curious at how this will turn out. I wonder if this is at all related to 
the problems we had with 8.4.1 causing read errors with the new read 
balancing settings when the OS cache is dropped.

I guess it would be pretty embarrassing if DRBD wasn't honoring fsync 
under certain kernel combinations. For what it's worth, we have 8.3.10 
on our existing cluster pending upgrade, and fsync times are definitely 
longer when both nodes are present. I wouldn't be surprised if something 
in kernel 3.2.0 causes a subtle break here.

That said, most of the complaints on this mailing list tend to 
concentrate on how slow DRBD has made an existing setup. Now you come 
along and start claiming the opposite. :)

-- 
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
312-444-8534
sthomas at optionshouse.com

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