[Linux-cluster] Cluster Planning

[pheeh at nodeps.org]

>From a newbie...
I am having the same concerns.  I have two boxes that are dedicated
storage (iSCSI), and two dedicated GFS servers so it looks like:
Storage Machines:
storage1
storage2

GFS:
gfs1
gfs2

Now, if I create the LVM on gfs1 and it encompases storage1 and storage2,
I would be able to mount the LVM on gfs2 via something like nbd or use
gfs1 as a iscsi target in itself.  However, lets assume that gfs1 just
dies.  Then the LVM on gfs1 would no longer exist and gfs2 would not be
able to write to the disks.
So I guess my question is could I create two LVM instances one on gfs1 and
one on gfs2 where each would have access to both devices such that:

gfs1 /dev/cluster/web (storage1, storage2)
gfs2 /dev/cluster/web (storage1, storage2)

So that either GFS server could croak and a web server would still be able
to access one of the boxes?  Although I don't see how that would work.

Now, I have figured out that with a single storage device its pretty
simple since both machines just mount the iscsi with the initiator,
although I just can't seem to figure out hwo to get it done with 2 storage
devices such that they act like a RAID1 and failover is seemless.

> Scott,
>
>
>
> On 4/20/06, Scott Kellogg <skellogg at egginc.com> wrote:
>>
>>
>>
>> The only problem you will encounter is that without a SAN you will
>> probably have to sincronize data between the servers if your application
>> stores data on internar discs on the servers....
>>
>>
>> Yes, this is the issue that seems to have multiple solutions.  I've
>> looked
>> at NFS, DRBD, rysnc, and Unison, but none of these technologies has
>> jumped
>> out at me as the best one.
>>
>
> Correct
>
> Also to use an active-active (same service active on both servers)
>> configuration + loadbalancing you will need more than 2 servers; at
>> least 4
>> servers, 2 for loadbalancing (1 active/1 backup) and 2 for the critical
>> service active concurently on both servers (no high availability, no
>> failover).
>>
>>
>> You seem to be referring to LVS.  Right, I can't implement that since I
>> don't have enough hardware.  I think that active-passive will be the way
>> to
>> go.  When the active node dies, the passive node will take over.  The
>> data
>> will only be as fresh as the last synchronization.
>>
>> That begs the question of what happens when the active node comes back
>> up
>> ... will the passive node (now active) sync its data to the new active
>> node?  This is where picking a synchronization method becomes vital.
>>
>
> Excellent point here.
> That's the problem when you dont have a SAN --> sync!
>
> Let's suppose we have a 2 node on failover.
> NodeA active NodeB passive.
> NodeA should be in sync with NodeB
> If NodeA dies, NodeB takes over
> NodeB must then continue to sync its data to NodeA (when it becomes
> available again)
>
> This a tough job!
>
> About the sync technologies you mentioned:
>
> DRBD
> When you will need a special kernel with support for that. Or recompile a
> new kenel (be careful since Red Hat wont support any modified piece of
> software you use, specially the kernel)
>
> NFS:
> You will need a dedicated server to provide shares, right?
>
> Rsync:
> Must have pretty intelligent scripts to garantee what we discussed above,
> and still not satisfactory
>
> /Filipe
>
>
>
> /Scott
>>
>>
>>
>> But if the active-active is for the servers (hardware), which means not
>> the same service on high availability  then; 2 servers doing
>> loadbalancing
>> (1 active/1 backup), 2 servers providing 2 critical services, one actice
>> on
>> node A and the other one active on node B (failover activated)
>>
>> Well thats my understanding about Red Hat's Cluster Suite... Please
>> correct me if I Am wrong...
>>
>> Att.
>> Filipe Miranda
>>
>>
>> On 4/20/06, Scott Kellogg <skellogg at egginc.com> wrote:
>> >
>> > Hello,
>> >
>> > I was wondering if I could get some assistance in setting up a two
>> > node cluster.
>> >
>> > We have 2 Dell PowerEdge 850 machines running RHEL4.  Our license for
>> > Cluster Suite is still in purchasing.  The main thing in the Cluster
>> > Suite documentation which confuses me is the use of a SAN.  RHEL4
>> > docs claim that the need for a SAN has been eliminated, but I'm
>> > having trouble find more information.  Most of the docs assume you
>> > are using a SAN. My customer could not afford the SAN, just the
>> servers.
>> >
>> >
>> > I would like to set up a high-availablity environment.  I understand
>> > that due to the hardware configuration (no SAN, no RAID) that there
>> > are still points of failure.  I'm hoping to set up a simple active-
>> > passive configuration.  We will be running LAMP applications.  If the
>> > primary server cannot deliver services, I'd like to automatically cut
>> > over to the backup.
>> >
>> > Ideally, I'd like to set up active-active and load balancing, since
>> > the servers have DRAC4 fence devices for use with STONITH.  However,
>> > since there is no SAN, I'm not sure how data will be mirrored across
>> > the two machines.
>> >
>> > Any help is appreciated!
>> >
>> > Thank you,
>> > Scott Kellogg
>> >
>> > --
>> > Linux-cluster mailing list
>> > Linux-cluster at redhat.com
>> > https://www.redhat.com/mailman/listinfo/linux-cluster
>> >
>>
>>
>>
>> --
>> Att.
>> ---
>> Filipe T Miranda
>> RHCE - Red Hat Certified Engineer
>> OCP8i - Oracle Certified Professional--
>> Linux-cluster mailing list
>> Linux-cluster at redhat.com
>> https://www.redhat.com/mailman/listinfo/linux-cluster
>>
>>
>> --
>> Scott Kellogg
>> System Administrator
>> EG&G Technical Services, Inc.
>> (812) 854-7077 ext. 236
>>
>>
>>
>>
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>> Linux-cluster mailing list
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>>
>>
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