[DRBD-user] Is `sync` option of ext3 mount SHOULD used in drbd HA clusters?

Pan'ko Alexandr A.Panko at infocom.dn.ua
Mon Sep 15 17:16:40 CEST 2008

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


В Пнд, 15/09/2008 в 16:11 +0200, Lars Ellenberg пишет:
> On Mon, Sep 15, 2008 at 04:43:49PM +0300, Pan'ko Alexandr wrote:
> > В Пнд, 15/09/2008 в 15:26 +0200, Lars Ellenberg пишет:
> > > On Mon, Sep 15, 2008 at 03:55:55PM +0300, Pan'ko Alexandr wrote:
> > > > Hi.
> > > > 
> > > > Let's see article from 
> > > > http://wiki.centos.org/HowTos/Ha-Drbd
> > > > 
> > > > Let's do commands:
> > > > 
> > > > [root at node1 /]# drbdadm primary repdata ; mount /dev/drbd0 /repdata
> > > > [root at node1 /]# dd if=/dev/urandom of=/repdata/test.file  bs=1000000c
> > > > count=1000; ip l set eth0 down;
> > > 
> > > 
> > > how about
> > >   dd ... conv=fsync
> > > 
> > > see also: man fsync
> > 
> > Of cause I now about this params.
> > But are you sure that Tomcat and Firebird know about it too? :)
> 
> that is _their_ problem.
> not drbd's.
> 
> if it has never been submitted to drbd,
> drbd cannot replicate it.
> as simple as that.
> nothing drbd can do about it.

DRBD _will_ work with them.
In case of no sync option it will be not reliable.
In case of sync option it _may_ work slowly.
It is all I want to confirm, because I do not see doc's and mails in
this list archive about such problem.

I hope you do not mean that I must fsync() after _every byte_ wrote.

If I cancel connection in progress of dd ... conv=fsync, I get the same
results as with no conv=fsync.

Please try yourself and only then write here.

> > By such commands I modeling the accident fail of one of peer in active
> > disk writes.
> > 
> > I know how to save files ;).
> 
> good.
> then don't complain that drbd does not replicate file you did not save.

It is live save. I act as normal program.
I did not say that "drbd does not replicate".
Drbd _does_ replicate but with no cache on ext3 filesystem.

I changed dd on simple cp command (cp /tmp/1.file /; ip l set eth0
down). And I do not see the file on other side at all. It is 73M length.
Moreover after I checked filesystem on other side - it says it is clean.

DRBD is very good project I did not saying anything bad about it.
I simply give facts.


-- 
Regards, Alexandr A. Panko



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