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!