[DRBD-user] Backup across wide area network

Lars Ellenberg Lars.Ellenberg at linbit.com
Tue Aug 16 19:16:27 CEST 2005

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

/ 2005-08-15 19:19:39 +0100
\ Timothy Arnold:
> Hello!
> I was just wondering what peoples thoughts were for backing up file
> servers/backup servers to a remote location across a wide area network
> (read +10mbps free). Has anyone ran into any issues with doing this?

if you consider drbd as desaster recovery measure,
yes that is possible.
there are implications, however.

the resulting maximum LATENCY is the sum of the maximum latency of the
local io stacks (probably neclectible) _plus_ the network link latency.

you should use protocol A (for lower latency), but you risk to lose some
"transactions" (i.e. for a file system: journal writes).
read: in case of failover, worst case you may need to run fsck, even
though you use a journaling file system.

the resulting maximum THROUGHPUT is the _minimum_ of the throughput of
the local io stacks and the network, so probably the network bandwidth.

so if you run drbd over a 10 mega bits per second wan link,
you get 1.2 mega bytes per second throughput at max.
that is round about the "speed" of an 8x cdrom ...
you know what I mean.

you could consider to run "disconnected" most of the time,
and do scheduled reconnects and resyncs.
you should snapshot the synctarget before it becomes synctarget.

you want to configure a small active set size (al-size).

drbd is _cleartext_, so if you store anything secret on that device, you
want to make sure that the drbd link is routed through some vpn.  maybe
your vpn has some compression options as well, so you may even get
better throughput that way.

you should consider wether rsync is the better tool for the job.

: Lars Ellenberg                                  Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH            Fax +43-1-8178292-82 :
: Schoenbrunner Str. 244, A-1120 Vienna/Europe   http://www.linbit.com :
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