Posts Tagged ‘General’

Stretched Clusters

February 1st, 2013

I’ve been having this discussion a lot with customers, and berating storage vendors for pretending that stretching a storage cluster makes everything fabulous! Generally I find this topic easiest to whiteboard, and with some fancy magnets here is the result of my first video blog. The sounds is a bit off, but hopefully you can still understand it all. 

Similar videos from storage vendors that don’t necessarily fully explain the limitations and problems…

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Functional Capacity

December 12th, 2012


It’s my job to size storage properly. How do I do that? Well, with a significant amount of faith in the vendors! Clearly we need an understanding of the existing footprint. Not just provisioned storage, but backup routines, actual used storage, database white-space, change-rates, data types and so on. It can actually be fairly complex if you need a detailed and precise sizing done. But let’s be honest, most customers haven’t the time or inclination to pay to do this, they’ll guess at a large growth figure (10% YoY or maybe 50% over 3 years), then we factor in a little contingency space and that gives us our functional capacity requirements that should have enough headroom to allow for any inconsistencies. Sounds like guess work? A certain amount is, yes :-)

So why am I saying functional capacity when most vendors sell us on usable capacity? Because usable capacity often doesn’t factor in any technology, so if I want snapshots, that needs capacity. Replication? A bit more. Clones? Obviously a bit more still. Then it can get more complicated, what RAID configuration, 10, 5, 6? What size RAID groups? Most people will take the vendors recommendations here, but do you trust the vendor? If its a competitive solution are you getting a good discount, or is the configuration changing to optimise the functional capacity without impacting their margin too much? Then there’s efficiencies, tiering (what’s your working data set?), deduplication (how much data commonality do you have?), thin provisioning (how much white space or over provisioned storage?). Also the data split, how many of your required IOPS should be served from SAS, how much is near-line, how much flash do you need to accelerate the lot?

NetApp Capacity Planner_v2 SAS

However, it’s incredibly difficult (sometimes impossible) to estimate functional capacity. What is your change rate? You have a NetApp today and the change rate is 2% weekly. How much of that is deduplicated? How will that change when you most to a different storage technology with a different stripe size and RAID configuration? You use clones today: what is the write and change-rate of those clones? What is the impact of moving from one RAID size / type to another? This is all very difficult to be exercise over. Sure experience will us to become clairvoyant and to predict what you require with relative accuracy, but this isn’t always accurate. This is why there is always significant headroom in any storage solution. This is why a lot of the vendor quoted storage efficiencies can often be difficult to prove as you’ll bake in a lot of headroom. No doubt this will allow an innovative group of sales people in a few years to come back and guarantee us x% efficiency over your existing solution.
This is also a very good reason why capacity-on-demand is becoming so popular! Predictable cost (even at an uplift) and additional capacity that is always available. There’s nothing worse than explaining that the system went down because you run out of disk space! But it means none of us have to spend too much time (and money) on giving a detailed capacity planning report, we can make some very educated assumptions and size against that. It’s only if you need specific guarantees or performance that you need to go into a bit more detail around analysing the existing estate, and even that is tricky, especially if there’s a bottleneck to day. I’m really hoping that with flash technology we will be sizing against capacity only, as performance is very difficult to size accurately against (more so than functional capacity!).
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What next for storage?

December 11th, 2012

Storage vendors have been very inventive over the years, creating some very interesting technologies: unified controllers, wide striping, various snapshot techniques, capacity efficiencies, etc. etc. But where has the key innovations been recently? Is it enough to have fancy features and technology? Is this what customers are even asking for?

The primary use case I still see for vendors is virtualisation, but you can probably suggest that databases are still a key business requirement for most organisations, and whatever we’re told, databases are still physical. So is there any major benefit in having fancy technology at the back-end of the storage with virtualisation in front?

Scale-Out Storage

Scale-Out Storage

First lets look at the database, as this is a relatively easy one to address. You could suggest that tiering is a great technology for databases, most data is historic and not read actively, most intensive applications will be accessing a small data set. But this is assuming that an application is written correctly and you aren’t doing full table scans, this is also assuming that you are regularly access this relatively small working set and that its predictable. Another key element is the high write throughout of logs and temporary databases. Tiering may fix a few use cases for data tiering of databases data, but it makes me feel uncomfortable and its not predictable, but this doesn’t fix my write requirements which require something with good write performance.

Really, to make the best use of a database you still need to be manually controlling the data and the disk configuration. High performance flash technology for write workloads, and split the database files up so that the active working set can always be addressed from flash also. This will not only give much more predictable performance, it should in many circumstances be as efficient and as dynamic as any tiering technology, just without the downsides (of which there are a few).

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DR to the Office

December 7th, 2012
Dilbert DR Plan

Courtesy of Scott Adams

If you don’t mind entertaining me, go into your data centre please. In fact first of all, when you refer to your data centre, in your head does it have inverted comma’s around it in a sarcastic fashion? Is it a “data centre” (roll eyes)? Now head into your “data centre”, how does the cabling look? Is every server dual connected to power supplies? Do you have a room UPS and advanced environmental monitoring to identify hot spots? You do? Great, stop reading this article as it’s not for you…

If you have a “data centre” and you’d be relatively embarrassed if someone started asking you about redundant power & cooling or when the last time your generator was tested (you have a generator right?) or your last security audit and pen-test, then please read on. I say or, but really that’s and/or but I don’t want this to sound like a census.

At VMworld last year we heard how fantastic SRM 5 is and that it enables service providers to start offering DRaaS (don’t get me started on **aaS) and how businesses will rejoice at this offering. There’s one hole in this concept for me I’m afraid however. You’ll be paying a service provider to host your DR that you use perhaps twice a year. This will be hosted in a top data centre, with fully redundant power, environmentals, fully diverse network, fully monitored, secure, audited, and so on. That’s what hosting providers do, they light up data centres and they choose the best as it’s their business to be the best. And your primary hosting will be out of your “data centre”. I think by now you know where I’m going with this, so I won’t labour the point too much. “Data centre” (roll eyes).

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Why do I finally care about Microsoft HyperV?

December 7th, 2012
System Center 2012

Microsoft System Center 2012

It’s not a secret that traditionally I’ve been a big fan of VMware and it’s product portfolio. But with the latest release of Microsoft’s extensive 2012 portfolio (the Systems Center stack and the Windows stack) I suddenly find myself unable to be dismissive of this stack any more. I’m not dismissing RHEV, Xen or Oracle for a second here either, I’m just focusing on VMware and Microsoft for various reasons (which I won’t go into here). Traditionally it’s been quite easy, although Microsoft had some great marketing around their private cloud technology it just wasn’t quite there for me at the hypervisor level, but 2012 fixes a lot of that! Just a quick overview of HyperV features that make it a contender.

  • Live Migration – functionally a good comparison with vMotion
  • Cluster Shared Volumes – a great alternative to VMFS and SMB support is exciting!
  • Dynamic Memory – we could argue all day as to why VMware’s memory technology is different / better than Microsoft’s and vice-versa. Simply put they do a very similar thing and net gains are going to be very similar. But server memory is cheap! And applications like Oracle, SQL and Java grab it all regardless and prevent any fancy hypervisor techniques.
  • Virtual Networking – Always one of my biggest complaints / criticisms with HyperV, but it seems Microsoft might just have finally fixed this.

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