HP has introduced server software-based dynamic provisioning for new EVA arrays; EVA Dynamic Capacity Management (DCM).

HP has followed the introduction of the XP 24000 with its controller-based thin provisioning, by extending a roughly similar capability to three new mid-range drive arrays, the EVA 4100, 6100 and 8100.

It does this by adding a software (SW) module to each Windows server accessing a networked EVA array. The SW module, working in conjunction with the host Windows O/S to rapidly and easily provision storage. This seems to be thin provisioning and has been referred to as such by HP people.

Rich Steffens, VP and GM for SANs, said that the latest version of Windows server has the ability to shrink a LUN. But it does not do thin provisioning itself. That is provided by the HP DCM software 'agent' which talks to firmware in the new EVA arrays.

This approach means that dynamically-provisioned EVA arrays are closely-coupled to specific versions of the Windows server operating system. In effect, HP is producing and relying upon agent software in EVA-accessing servers. Because it is HP-produced software then it won't be available for customers not buying the new EVA arrays.

Tony Asaro, an ESG analyst, said: "It's not thin provisioning. You can't over allocate capacity to a server." According to this view DCM is 'thin provisioning lite.' Baeverstad called it 'adaptive provisioning.'

Traditionally an application is allocated a LUN with the full amount of storage capacity needed, say 20GB. With thin provisioning it is actually given a fraction of this, say 5GB, but spoofed to believe it has the full 20GB. Then, when the 5GB is nearly filled up with data another 5GB will be given to it.

Across a set of servers a large amount of disk space can be saved. This means customers don't have to buy as much disk space as they would have had to do before.

The thinking here is that LUN set up is difficult and not to be messed with. DCM alters this. Kyle Fitze, HP's director for SAN marketing, said that it makes expanding a LUN easy. Therefore 5GB can be allocated at first. Then, when more capacity is needed, the LUN is simply expanded by another 5GB.

So, if there is a need for more mailbox space, Exchange's LUN is simply increased in size.

The effect on actual disk capacity needed is the same but the method of achieving it is differerent. Where HP says DCM is better than thin provisioning is that LUNs can be dynamically shrunk, decreased in size, as well.

Ash Ashutosh, HP's chief technologist, said EVA-using applications like Exchange and SQL need to be able to grow and shrink LUNs. But XP-using applications do not.

The thin provisioning technology was pioneered by 3PAR with its InServ array products.

HP's EVA dynamic provisioning implementation is not open and requires server (host)-based software, equivalent to driver code. It provides the capability for a LUN to be dynamically expanded, as does the XP implementation, or shrunk, which is something the XP implementation simply cannot do.

HP is providing its dynamic provisioning capability for Windows first since, as Mark Gonzalez, responsible for HP servers and storage sales in the Americas, said: "Most EVA sites are running Windows."

He said: "Other operating systems support will follow in due course," referring to Unix (HP-UX), Linux and OpenVMS. Harry Baeverstad, SMB busines director for HP, said HP-UX and Linux will be next with OpenVMS following after them.

Steffens added that, regarding providing DCM for Linux:"We'll make the software open source and write it into the kernel."

Two technologes

HP also now has two 'thinnish' provisioning technologies: the HDS-supplied XP24000 one; and the EVA HP server software-based one. The XP technology is completely independent of accessing servers and can be applied to arrays virtualised behind the XP24000 controller (such as an EVA array if desired). The EVA version is specific to Windows servers with the HP software module and has the additional capability that LUNs can be dynamically decreased in size which the XP implementation cannot.

For customers running both XP and EVA arrays HP has just introduced two different and incompatible 'thin/adaptive' provisioning technologies. This is counter to HP's professed aim of moving from high-cost islands of IT resource to low-cost pooled islands of resource.

Steffens said that although HP customers may often have both XP and EVA arrays they are generally used for separate application areas. This agrees with Ashutosh's point. The implication of this is that are separate islands of storage and so different ways of providing capabilities don't matter.

The thinly-provisioned EVA arrays do represent a lowering of cost, since not so much capacity needs to be purchased up front, but the thinly provisioned EVA is a separate island of thin provisioning from the XP24000.

With dynamic provisioning for EVA arrays HP has introduced a much more economical way to buy EVA capacity and defer up-front purchases. It also enables customers to match power needs much more closely to the disk space actually needed for their current data, meaning that they will be spinning far fewer empty disk platters and saving money on array cooling as well.