A drive array controller presents its component disks as, well, component disks, and carries out I/O from them to the outside world. It can also virtualise the disks behind it. This is what IBM’s ESS, or Shark, high-end arrays do. The DS8000 goes a step further. As does HDS with the controller inside its TagmaStore enterprise array

Submit to HDS head
Hitachi Data System’s TagmaStore arrays employ a Universal Storage Platform (USP). What’s ‘universal’ about an array controller? The short answer is linking to external storage arrays as well as the HDS drive arrays. Scott Genereux, HDS senior VP for global marketing and channels, says it can provide “New levels of virtualisation and replication not possible in previous generations of enterprise storage.” It can pool together both internal – that’s HDS’ own drive arrays – and external storage into a single virtual set of storage blocks, up to 32 petabytes of them.

The external arrays are linked in by 2Gbit/s Fibre Channel links and operate within the TagmaStore environment. HDS says that, by using its own replicator software on the USP customers can avoid paying license fees for it in the subordinate arrays. Ditto maintenance fees.

The virtualisation means that internal and external storage resources, including ports, cache and disk, can be grouped into Private Virtual Storage Machines or partition. These could be based on different tiers of storage and provide a basis for information lifecycle management.

The HDS idea is that, instead of having several arrays with several independent controllers, you subsume them under one head controller. Brian Frank, a senior architecture and infrastructure director for United Airlines offered this supporting thought; “As we all know, anything with more than one head is a monster.” The non-HDS arrays become submissive resources under HDS direction.

Array controller or server?
IBM’s new high-end DS8000 doesn’t have any old storage controller. It uses the newest Power5 server chip and comes in dual and quad cpu versions. Its architecture can scale to three times the TagmaStore limit of 32PB, that’s 96PB. Expect an 8-way version to extend the current 192TB limit of the 4-way DS8000.

Similar to TagmaStore the 4-way DS8000 models can have their storage resources split into logical partitions or LPARs.

The use of Power5 cpus means that storage applications can be run inside the DS8000 controller, such as Vertitas’ backup products. We might also consider IBM’s own San Volume Controller. Interestingly the latest version of this supports IBM DS8000 and DS6000 arrays as well as EMC’s DMX arrays, HP’s EVA arrays and some HDS arrays. We could be facing a situation where an IBM DS8000 could have an HDS array submissive to it or vice versa!

The DS6000, IBM’s modular array and EMC CLARiiON competitor, shares micro-code with the DS8000 and runs the same operating environment so the linking of the two together to provide a dual storage tier within a single virtual pool also becomes a possibility.

Who needs intelligent switch platforms?
Brocade, Cisco and McDATA are promoting the idea of intelligent switch platforms to provide SAN storage applications. Virtual tape drive applications, such as IPStor, have been mentioned. The idea, again, is to relieve host servers of SAN storage application responsibility and move towards a utility-like storage resource. Inside this resource data is protected, it is hosted on the appropriate tier of storage, it is migrated from tier to tier using policies. The actual storage resource is virtualised to minimise wasted disk blocks. The whole utility is managed through one pane of glass.

What we are seeing now is the first response to the idea of intelligent platforms inserted into the SAN to carry out these functions. And the response is to insert these platforms into the SAN:array controller interface.

In effect the storage application processor is stuck onto a SAN switch or director, or an array controller. The overall functionality is largely the same; it’s just the location that’s different. HDS’ approach already includes linking to external arrays from the TagmaStore array and providing a single virtual resource. When we see tape libraries so linked and disk-to-disk backup provided then things will be clearer still.

IBM still has to actually say it can support external links and can virtualise across them using the DS 8000 Power5 controller. There seem to be sufficient clues around to indicate that this is part of IBM’s roadmap though.