Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On Thu, May 10, 2007 at 10:44:58AM +0100, Mark Watts wrote:
>
> > Hi all:
> >
> > I have no idea about how long the primary sync its data to secondary?
> >
> > Or once the data is changed on primary physical device, it is send to
> > secondary immediately?
>
> Data replication is basically real-time, within the constraints of network
> bandwidth and raw I/O performance.
>
> In the "resource" section of /etc/drbd.conf, you define the transfer protocol
> to use for that resource (/dev/drbd0 for example).
>
> It can be one of the following three:
>
> C: write IO is reported as completed, if we know it has
> reached _both_ local and remote DISK.
> * for critical transactional data.
* for most cases.
>
> B: write IO is reported as completed, if it has reached
> local DISK and remote buffer cache.
* for cases were you can live with possible data loss
of the last few milliseconds in case of failover
we should improve our documented recommendations :)
> A: write IO is reported as completed, if it has reached
> local DISK and local tcp send buffer. (see also sndbuf-size)
> * for high latency networks
>
> If you choose C, then write a file to the DRBD'd filesystem,
> the write won't
and then fsync! otherwise the write goes
just into the local nodes cache,
and drbd knows nothing about it yet...
> return (ie: the command won't complete) until the data is written to both
> local and remote disks.
>
> Mark.
>
> --
> Mark Watts BSc RHCE MBCS
> Senior Systems Engineer
> QinetiQ Trusted Information Management
> Trusted Solutions and Services Group
> GPG Key: http://keyserver.veridis.com:11371/search?q=0x455420ED
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