[DRBD-user] file replication between sites
Lars.Ellenberg at linbit.com
Wed Mar 7 12:42:55 CET 2007
/ 2007-03-05 17:07:06 +0100
\ Kristian T Knudsen:
> We have been waiting for years to have a setup that can replicate our
> project files between our sites through 2-4Mbit dsl (max 30sek. delay).
so for synchronous (drbd protocol C) or "quasi synchronous" (drbd protocol A)
replication, you'd have sustained write throughput of max 200 - 500 kByte/sec
you should have an application that would not really write too much.
> I read that version 0.8x would have the feature that you can mount the
> disks from both sites and thus write to the disks from both sites at the
> same time and the changes would be replicated back and forth.
yes, when you use a cluster file system. I'd consider it "experimental"
to use cluster file systems over WAN, though.
> We are looking for the simplest setup first, 2 node active-passive
> cluster (sles 10, heartbeat) and a DAS disk system connected to both
> serveres. This setup on 2 different locations with 500km between them
> (Tinglev, Denmark and Berlin, Germany). We have a dedictated E1(~2mbit)
> line with about 25ms delay for the data transmission. The disks are
> about 500GB and the data generated each day is about 500MB, but the data
> change is a lot more we assume serveral GB/day. Also noteworhty is that
> we have millions small files (10-50kb).
normal local scsi disk:
latency ~ 2 to 3 ms, throughput ~ 100 MegaByte per second
good local raid system with battery backed write buffer and stuff:
sub millisecond, 200 MegaByte per second and more
LAN, GigE: rtt ~ 0.2 ms, ~ 100 MegaByte/second
your line: 25ms rtt, ~ 200 KiloByte / second
so, if you run drbd on top of your line,
you'd have about whatever your local readperformance would be.
but your write performance would feel like one of those
first generation CD writers.
the maximum you could expect for a 2Mbit line when it transfers at its
limits 24 hours: about 16 GByte per day.
> Later we would connect a third site to this setup and replicate
> between them. Perhaps in the future also use ocfs2 to make it
> active-active on each site with the 2 node clusters or do I actually
> need to make use of the clsuter file system now to be able to it in
> the first place?
you should use OCFS2 right away, if you intend to somewhen use it
active/active. But given the circumstances, I won't recommend this.
one network glitch, and ocfs will do a self-fence :-/
> The main part is that the files are kopied between sites and replace
> older versions and that when you open a file on one site, that you on
> another site can se it is opened from someone with the fil-locking
> feature from dedicated applications such as AutoCAD, which uses .DWL
> "(DraWing Lock) files are temporary lock files created when a drawing
> file (.DWG) is opened."
> So the obvious question ... is that possible with 8.0.1, and has someone
> by any change a similar setup that has it working?
it would be possible.
but my understanding of AutoCad and similar, is, that it produces and
handles potentially large files, changes some small things in it,
and then writes it all back to disk.
what you'd probably need is some asynchronous file based rsync-like
replication triggered by file system events.
if you contact us at LinBit, we might be able to tailor something for
you with the semantics you need based on our csync2 ...
: Lars Ellenberg Tel +43-1-8178292-0 :
: LINBIT Information Technologies GmbH Fax +43-1-8178292-82 :
: Vivenotgasse 48, A-1120 Vienna/Europe http://www.linbit.com :
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