Gavin W. Burris on 12 Dec 2010 14:38:50 -0800

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Re: [PLUG] 3-way data mirror?

DRDB does a raid mirror over the network, at the block level.   This is
not what you want, since you can't mount the same block device
read/write at more than one location.  You have to mount a formatted
block devices, say as ext3, then export it via nfs.  The nfs server
would then allow multi-client read/write access at the file level.

Mounting nfs at two different locations would be extremely slow and
insecure, unless there was a high-speed dedicated fiber link with
private vlan.

Methodic use of a file synchronization tool such as rsync with the
"--update" option, or Unison, would be a good option if locking is
considered.  So would a revision control system, like Subversion, if the
files aren't too big.  In both cases there would have to be a master
repository that the multiple sites sync to/from.


On 12/12/2010 04:23 PM, Eric at wrote:
> This is a wild guess but perhaps DRBD would work?
> If you could set up a VPN with appropriate QOS and get a fast enough link... ?
> Just a thought.
> Eric
> On 12/12/2010 12:52 AM, JP Vossen wrote:
>> I have a situation where I have 2 labs that need to keep ~150G of data in sync,
>> but they can't talk to each other.  They can talk to a 3rd machine, which is
>> also backed up, so...
>> What I think I'd like to do is have:
>>     Lab1 <--> COLO <--> Lab2
>> The problem is that lab1 and lab2 are both read-write, so there is a real
>> possibility of stepping on changes.  COLO is read-only.
>> I'd try to just relay through the COLO, but that's also where the backup will
>> happen.  And I can't get the FW rules changed.
>> Any better ideas?
>> Any suggestions on tools?  I'd strongly prefer something already in the CentOS-5
>> or EPEL repos.
>> Thanks,
>> JP
>> ----------------------------|:::======|-------------------------------
>> JP Vossen, CISSP            |:::======|
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Gavin W. Burris
Senior Systems Programmer
Information Security and Unix Systems
School of Arts and Sciences
University of Pennsylvania
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