UNIX-DATABASE QUESTION

[Javier Ortiz Guajardo]

Maybe it is a silly question, but anyway..here you are.

Informix database has a functionality that allows to run the database in two servers and can be acces the same disk array at the same time, The question is, could unix work with this type of functionality? could the Volume Groups be active on both servers?
Do you think that it could works in two unix servers (v2250)?

Thanks.

[Rajeev Shukla · Accepted solution]

Pardon me if i am wrong, but what i understand from you'r query is that you are running informix server on 2 servers and want to sore the database at one place like a parallel server (like Oracle parallel server i guess). This functionality is not within Unix, but is the feature of Database like the Oracle parallel server does.
Because what i am sure is you can not activate a volume group on 2 servers at the same time for writing. What you can do is activate on one server with read-write and other server as read-only.

I hope that make the point clear.

Cheers
Rajeev

[Steve Lewis]

As has been said, Informix XPS does allow you to have a distributed databases and distributed tables, which have parts on different machines. But this is all synchronised over the network. It does NOT share the same volume group or logical volumes and it will not work if you try. You will corrupt data if you activate the same VG on both servers simultaneously then start informix.

Oracle, on the other hand, does allow you to share data, using MC/Serviceguard volume group activation in shared mode. It handles its locking on the disk array, which used to be more efficient that the network based transaction model, but now with multi-Gigabit networks the improvement may be less distinct.

If you have a single array with separate LUNs in different volume groups on each machine, you will be able to use informix XPS and distribute your data.
Then if you add Serviceguard to that, you will be able to make each server contingent to the other using floating IP addresses and exclusive access to the volume groups, so that the database is up 100% of the time. Just don't allow a volume group to be activated on both machines at once. This is a big project and needs planning and testing.

[A. Clay Stephenson]

Actually two (or more servers could activate the same VG at the same time) and could be made to work and play well with others but it requires very careful programming AND it requires that all I/O be done using raw devices --- no filesystems. (Actually, Veritas has a filesystem that will allow it as well but I would distrust it on general principles.) THe fundamental problem is not one of simultaneous disk access as much as it is buffer cache consistancy. The problem is that Server A will make a change to its buffer cache and serverB will know nothing about it. Using filesystems will rapidly result in absolute chaos BUT because raw devices use no buffer cache then it's at least possible to do this acthough it still requires very careful attention to synchronization issues.

[Christian Gebhardt]

Hi

I have attached a document about Oracle RAC.

Short summary, Unix can - but it is expensive.

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For all, which are interested in RAC:

We are testing RAC at this time. We won't spent much money, so we are using the following configuration (only supported for testing):

- 2 machines, with firewire (500MHz, 256 MB, Suse SLES 8)
- 2 network cards for each machine (1 for Cluster interconnect, one for the public network)
- external firewire rack with IDE-Harddisks
- Oracle 9i Software
- Oracle 9i RAC Firewire Patch

Oracle works with OCFS (Oracle Cluster File System)

Chris