Take it from me, SMI-S is a thing of the past. If there’s one thing the last few months have taught me it’s how different each vendor’s products really are. I’ve been working on a tool called SRA (see the link here) which will report on storage in a consistent manner. Let me tell you that isn’t easy…
- EMC Symmetrix/DMX – Physical disks are carved into smaller segments called hypers. These are then recombined into LUNs which then might be recombined into composite devices (metas) and replicated, cloned or snapped. The hypers that make up a LUN can come from anywhere within an array and can be moved around at will by a tool designed to improve performance, completely ruining your original well-planned configuration. Combining hypers give you RAID, which wasn’t RAID before and was something called mirrors but is now, and is even RAID-6! Devices have personalities which survive their presentation or removal from a port. A device can have multiple personalities at the same time. LUNs use a nice numbering system based on hex – but don’t expect them to number nicely if you destroy and create devices. Bit settings (flags) are used to ensure host SCSI commands work correctly.
- HDS USP/HP XP – Physical disks are grouped into RAID groups from which LUNs are carved. Until recently you couldn’t span RAID groups easily (unless you were combining some free space in each RAID group). Devices don’t have a personality until they’re presented to a host on a port, but they can have multiple personalities. HDS use a form of punishment known as CCI for anyone foolish enough to think they had made their arrays easy to manage. LUNs are numbered using a relic of the mainframe and yes, you can move things around to balance performance, but don’t think you can do it unless there are spare LUNs (sorry LDEVs) around. Different host types are supported by a setting on a host group which lets you confuse the hell out of every one by telling them their LUN numbers are all the same but unique. Oh, and the storage the user sees doesn’t actually have to be in the array itself.
- HP EVA – Phew! Physical disks are managed in groups (which it’s recommended to only have one of, but you can have more if you really must) but they don’t use RAID at the group level because that would be too easy. Instead disks are grouped into Redundancy Storage Sets, which reduce the *risk* of disk failures but don’t protect directly against them. LUNs are created only when they need to be presented to a host and they don’t have simple LUN numbers, but rather 32 digit UUIDs. RAID protection is done at the LUN level, making it more difficult to conceptualise than either of the previous two examples.
- Pillar Axiom – now we’re getting really abstract. With Axiom, you can tier data on different levels of performance, but wait for it – they will be on the same drive, but utilising different parts of the same spindle! Argh! Enough!
Clearly every vendor wants to differentiate their product so you’ll buy from them and not the competition. In some respects they *have* to differentiate otherwise all the vendors would spend their time in litigation with each other over patent copyright! (wait a minute, they already are). So SMI-S or any other standard is going to have a near impossible time creating a single reference point. Add to the mix the need to retain some competitive advantage (a bit like Microsoft holding back the really useful API calls in Windows) and to sell their own management tools and you can see why SMI-S will be at best a watered down generic interface.
So why bother. There’s no benefit. Every vendor will give lip service to the standard and implement just what they can get away with.
The question is, what would replace it? There’s no doubt something is needed. Most SRM tools are either overbloated, poorly implemented, expensive, or plainly don’t work so some light touch software is a must.
I think the interim solution is to get vendors to conform to a standard API format, for example XML via an IP connection to the array. Then leave it to the vendor how to code up commands for querying or modifying the array. At least the access method would be consistent. We don’t even see that today. All we need now is an acronym. How about Common Resource Access Protocol?