[Linux-cluster] using lacie ethernet disk raid as shared storage

[Gordan Bobic]

On Thu, 25 Jun 2009 13:15:56 +0200, ESGLinux <esggrupos at gmail.com> wrote:
> 2009/6/25 Gordan Bobic <gordan at bobich.net>
> 
>> On Thu, 25 Jun 2009 12:38:04 +0200, ESGLinux <esggrupos at gmail.com>
wrote:
>>
>> > I can mount this disk with NFS (also with CIFS but I´m not using this
>> > protocol)
>> >
>> > My idea was to mount the disk with NFS on the 2 nodes of a red hat
>> cluster,
>> > but I don´t know if it is a good idea. (perhaps no :-( )
>>
>> There's no reason why you couldn't or shouldn't do this. If all you want
>> is
>> some shared storage and don't care about the single point of failure,
>> then
>> this is exactly what the device was intended for. :)
> 
> 
> ok, I´m always afraid with data corruption and thougth I will have
> problems with this, but If you think that there is not problem I´ll
folow your
> advice ( at my own risk of course, ;-)

NFS is designed for concurrent access, it shouldn't cause corruption. And
anyway, your apache web data is likely to be read-only in most cases
anyway. Don't put things like database files into shared access areas,
though - that generally won't work, and even when it does, performance will
be appalling.

>> > The cluster are going to serve a HA httpd service (I know, with this
>> > disk I
>> > have a SPOF, but that is all I have, no money for more .-(( )
>> >
>> > any suggestion with this scenario?
>>
>> It should "just work" as you described. NFS mount it on both nodes and
>> point Apache at it as per usual. It'll probably work faster than a
>> clustered file system solution. For redundancy, however, if you have
>> enough
>> disk space on the web nodes, you could set up mirrored storage using
DRBD
>> and run GFS on top of that. You'd end up with full redundancy and no
need
>> for the NAS (assuming, as I said, that nodes have enough space). Note
>> that
>> fencing would be absolutely mandatory if you use GFS or else either node
>> failing would halt the cluster to prevent data corruption.
>>
> 
> I was allways looking for an oportunity to test DRBD. I think now is the
> moment. My reference web about DRBD is http://www.drbd.org/, any advice,
> read,  before I begin to test it?

That is, indeed, the right site. Stick to the docs, they are pretty good.
If you are going with this solution, you may also want to look into Open
Shared Root (http://www.open-sharedroot.org/). It should save you some
admin overhead since you can get away with using a single root fs for
multiple nodes. Just make sure your fencing works. But if you are new to
clustering, you may not want to dive straight into OSR - there are
potential pitfalls that aren't always entirely obvious. There are mailing
lists for both DRBD and OSR, so if you run into problems and the docs don't
provide an obvious answer, you can always ask there.

Gordan