Enterprise Computing: DMX-4 Is Dead – Long Live DMX-5!

Chris Mellor posted a great article recently, speculating on the future of certain storage products.  He hinted at a new high end array from EMC, presumably an extension to the DMX range – tentatively titled DMX-5.  

We’re about due for a new hardware release.  Looking back, the schedule has been:

• DMX-4 – 16th July 2007
• DMX-3 – 25th July 2005
• DMX-2 – 9th February 2004
• DMX – 3rd February 2003
• Symm 5.5 – 10th September 2001
• Symm 5 – April 2000

So, expect a new array announcement around June/July this year.  I’ve heard rumours of customers with secret EMC arrays, however they could have turned out to be Atmos and therefore just a bit of hot air.  Alternatively, they may have been the new DMX-5 – although I’ve not got any proof to back that theory up.

Will EMC retain the DMX/Symmetrix heritage or will they take the opportunity to leapfrog the competition with something new?

 The current DMX range suffers from a number of issues.  The underlying architecture uses the concept of hypers to create LUNs, so RAID is based on creating LUNs from discrete slices of a disk.

Problem 1: As hypers are used to create LUNs, a LUN will consist of a maximum of eight hypers across 8 disks using RAID-5 (7+1).  Creating these LUNs means making a hyper of a size which is divisible by the intended LUN size, so if you want a LUN of 70GB on RAID-5 7+1, then you need to create eight 10GB hypers.  If you want to stripe across more devices, then you have to go with meta-devices, which concatenate more than one LUN together.  This means either bigger LUNs or carving smaller hypers.  Typically though, an array configuration will be pre-determined at installation time and making changes to hyper sizes can be a torturous process, which is usually avoided. 

Problem 2: Legacy Code.  Symmetrix and DMX all worked off the concept of physical mirrors of a logical LUN – commonly known as mirror positions.  A BCV and an SRDF device become a mirror position, with a maximum of four permitted.  Without me offending the excellent programmers who have crafted the Enginuity microcode, EMC have had to effectively shoehorn new features in – for example Snaps & Clones to replace BCVs and Thin Provisioning.  The inherent Symmetrix/DMX design doesn’t lend itself to the implementation of new features.

 So, will EMC make a break and go for a complete redesign for DMX-5?  Wide striping seems essential, as does dynamic LUN creation, however top of my wish list is the ability to move data between tiers of storage within the same array – and for this to be granular enough to make it useful.

This requirement leads on to full policy-based placement of data and automated migration between tiers to maintain the service level requirements of the policy.  In turn, this leads to integration with Atmos, providing a full end-to-end policy-based data placement and management.  Wouldn’t that be good!

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