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

Lars Ellenberg lars.ellenberg at linbit.com
Mon Sep 15 15:26:43 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.

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

> [root at node1 /]# ls -l /repdata/test.file
> -rw-r--r-- 1 user users 1000000000 Sep 15 15:07 /repdata/test.file

thats all in page cache still.

> [root at node2 /]# drbdadm primary repdata ; mount /dev/drbd0 /repdata
> [root at node2 /]# ls -l /repdata/test.file
> -rw-r--r-- 1 user users 868456004 Sep 15 15:07 /repdata/test.file
> As you will see there will be different sizes.
> But they SHOULD be the same.
> If we will add to mount command the option '-o sync', than there will
> be no differences in sizes. But in case of 'bs=1c' in dd command the
> file creation will be very and very slow because of turned off chaching.
> Anybody knows this issue?
> SHOULD I turn off caching om ALL underling devices and filesystems to
> get HA cluster filesystem?

: Lars Ellenberg                
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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