I'd thoroughly agree with their recommendation.
DB2 on Linux (especially on x86-64 boxes with dual cores) rocks.
I came from a mainframe background too, with my first experience of DB2 way
back in 1989. I got into "the other DB2" before it was even known as DB2 :
OS/2 Extended Edition was where it all started back in the early 90s.
DB2 for Linux, UNIX and Windows is a very powerful product. I've used it on
AIX, Solaris and since it came out in a beta release at V6 level on Linux.
I've had my first production Linux site running since about 1990 (and a
number more since then).
As far as high availability is concerned, you have a number of upgrade paths
in DB2. You'll have to go beyond DB2 Express-C (the free version) for the
best of these. In my opinion this is HADR (High Availability Disaster
Recovery) which is dead easy to set up and gives exceptional resilience.
With V9 you have the full range of clustering options : a "share nothing"
version (DPF = Data Partitioning Facility), range partitioning (similar to
partitioning on mainframe DB2, but implemented better) and Multi-Dimensional
Clustering. You can even mix all three.
Replication is also available, in two flavours. SQL based replication (which
just about everybody has these days) and QRep (Queue Replication, using MQ
message queues as the transport mechanism). For the latter I know of at
least one banking installation doing over a million transactions an hour with
I've just started working, in the last few months, with RoR and DB2. I've
never had any difficulties. Thankfully I have good access to the folks in
the Toronto labs who develop the ibm_db2 adapter, and they have been most
helpful. I've made a few adjustments to the RoR code to make generation of
DB2 projects better : I've still to feed these through but I can share them
with you if you want. I've also been offering suggestions for improving the
If you are doing XML you'll also love the new hybrid relational and XML engine
in Version 9. You can mix and match SQL and XQuery to your heart's content.
You can index XML documents as well as relational tables. It stores the XML
in a properly parsed XML format, rather than a veneer on top of a LOB column.
Final note : the free version of DB2 is much less restrictive than the free
Oracle (and SQL Server). In particular there is no limit on the database
size. 4 gig of data only is a big restriction in a lot of situations, so
you'd have to buy an Oracle licence a lot sooner (and at a lot more per
licence too : especially if you tally up the cost of all the extras it takes
to get to the equivalent DB2 functionality !!!