Almost five years ago IT Week took delivery of a Clariion disk array from Data General. They are relatively small - ours had 10 disks - but use very high-performance cache controllers and Fibre Channel interfaces all the way through to the disk drives. Many disk arrays use Fibre Channel interfaces to link the cache controllers to the servers, but they rely on cheaper SCSI interfaces between the drives and the controllers.
Anyhow, not long after the Clariion arrived, Data General was acquired by EMC. Although the Clariion brand name has survived, EMC subsequently updated the design of the Clariion cache controller with a more powerful and completely incompatible CPU.
Of course, problems of obsolete IT systems are common, and occur for all sorts of reasons. In the case of our Clariion, the new type of processor enabled the cache controller to take on a bigger workload, which no doubt enabled the new products to offer more features. But the new chip also made it virtually impossible to maintain software compatibility between the new products and the older ones. The result was that #50,000 worth of storage hardware was gradually rendered almost completely useless.
EMC's latest storage management software, EMC ControlCenter Open Edition, is able to monitor our Clariion array, and can perform basic tasks such as LUN masking and zoning. However, ControlCenter can do all sorts of things with other EMC arrays that it cannot do for the older Clariions.
Still, why worry, because if the claims of the storage virtualisation vendors can be trusted, we can all forget about using the manufacturer's software to manage our storage systems. Instead, we could use a virtualisation system from just about any vendor to manage the Clariion storage.
Even without our problem with fading Clariion support, storage virtualisation sounds great. Imagine being able to make the most of all those expensive arrays of hard disks that are currently operating at far less than 100 percent utilisation. The trouble is, whenever we get a storage virtualisation system in for evaluation, the manufacturer starts explaining why the product cannot work with our disk array.
It's at this point that I am reminded of some recent correspondence concerning iSCSI. The analysts say iSCSI will be the next big thing in storage, bigger even than virtualisation. While storage virtualisation promises to centralise the management of expensive storage hardware into a single console, iSCSI promises to make the Fibre Channel networks of SAN systems obsolete.
Even so there seems to be some doubt about iSCSI. Rather than buy expensive solutions that might soon be obsolete, some firms prefer to focus on low-cost systems built with open technologies. ISCSI is an industry-standard specification, so it is open; but many of the first iSCSI products are only supported if they are used with iSCSI products from the same vendor.
In other words, despite the claims from vendors, neither iSCSI nor storage virtualisation seem to be ready for prime time.
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