Mind the UNMAP Impact On Performance In Certain Scenarios

The Problem

Recently we’ve been trouble shooting some weird SQL Server to file backup issues. They started failing on the clock at 06:00 AM. We checked the NICs, the switches, the drivers, the LUNs, HBAs, … but it was all well. We considered over stressed buffers as the root cause or spanning tree issues but the clock steadiness of it all was weird. We tried playing with some time out parameters but with little to no avail. Until the moment it hit me, the file deletions that clean up the old backups!We had UNMAP enabled recently on the SAN.

Take a look at the screenshot below an note the deletion times underlined in red. That’s with UNMAP enabled. Above is with UNMAP disabled. The Backup jobs failed waiting for the deletion process.

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This is a no issues if your backup target is running something prior to Windows Server 2012. if not, UNMAP is disabled by default. I know about the potential performance impact of UNMAP when deleting or more larger files due to the space reclamation kicking in. This is described here Plan and Deploy Thin Provisioning under the heading “Consider space reclamation and potential performance impact”. But as I’m quite used to talking about many, many terabytes of data I kind of forget to think of 500 to 600GB of files as “big” Embarrassed smile. But it seemed to a suspect so we tested certain scenarios and bingo!

Solutions

  1. Disable the file-delete notification that triggers real-time space reclamation. Find the following value HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlFileSystemDisableDeleteNotification and set it to 1.

    Note that: This setting is host wide, so for all LUNs. Perhaps that server has many other roles or needs to server that could benefit from UNMAP. If not this is not an issue.  It is however very efficient in avoiding issues. You can still use the Defragment and Optimize Drives tool to perform space reclamation on-demand or on a scheduled basis.

  2. Create LUNs that will have high deltas in a short time frame as fully provisioned LUNs (aka thick LUNs). As you do this per LUN and not on the host it allows for more fine grained actions than disabling UNMAP.  It makes no sense to have UNMAP do it’s work to reclaim the free space that deleting data created when you’ll just be filling up that space again in the next 24 hours in an endless cycle. Backup targets are a perfect example of this. This avoid the entire UNMAP cycle and you won’t mind as it doesn’t make much sense and fixes you issue. The drawback is you can’t do this for an existing volumes. So it has some overhead & downtime involved depending on the SAN solution you use. It also means that you have to convince you storage admins to give you fully provisioned LUNs, which might or might not be easy depending on how things are organized.

Conclusion

UNMAP has many benefits both in the physical and virtual layer. As with all technologies you have to understand its capabilities, requirements, benefits and draw backs. Without this you might run into trouble.

Join me for aTechNet Live Meeting: Hyper-V Storage Efficiencies & Optimizations in Windows Server 2012 R2

So you have been  playing with or down right seriously testing Windows Server 2012 and perhaps even Windows Server 2012 R2. That’s great. Many of you might have it running in production or are working on that. That’s even better.

Windows Server 2012 has brought us unseen capabilities & performance enhancements that make it a future proof fundament for many versions to come and it is ready for the ever accelerating pace of hardware improvements. R2 has fine tuned some points and added improvements that are stepping stones to better today and even greater in vNext. I’d like to invite you to a free TechNet Live Meeting on Hyper-V Storage Efficiencies & Optimizations in Windows Server 2012 R2 and look at some of these capabilities with me.

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As a virtualization guy two subjects are very dear to me and that is networking & storage, and this event is about a subset of the storage improvements. You might have heard about ODX and UNMAP but you have not had the change to play with it. You have read about the tremendous scalability of the IOPS in a VM and about large sector support for the next generation of hard disks drives. Well some of these we’ll demonstrate (ODX, UNMAP, Dynamically expanding VHDX performance) if the demo gods are with us. Others we’ll discuss so you’ll know where this comes into play and how you’ll benefit from them even without realizing you do. So without further delay register for the free TechNet Live Event here.

Future Proofing Storage Acquisitions Without A Crystal Ball

Dealing with an unknown future without a crystal ball

I’ve said it before and I’ll say it again. Storage Spaces in Windows Server 2012 (R2) is are the first steps of MSFT to really make a difference (or put a dent into) in the storage world. See TechEd 2013 Revelations for Storage Vendors as the Future of Storage lies With Windows 2012 R2 (that was a nice blog by the way to find out what resellers & vendors have no sense of humor & perspective). It’s not just Microsoft who’s doing so. There are many interesting initiatives at smaller companies to to the same. The question is not if these offerings can match the features sets, capabilities and scenario’s of the established storage vendors offerings. The real question is if the established vendors offer enough value for money to maintain themselves in a good enough is good enough world, which in itself is a moving target due to the speed at which technology & business needs evolve. The balance of cost versus value becomes critical for selecting storage. You need it now and you know you’ll run it for 3 to 5 years. Perhaps longer, which is fine if it serves your needs, but you just don’t know. Due to speed of change you can’t invest in a solution that will last you for the long term. You need a good fit now at reasonable cost with some headway for scale up / scale out. The ROI/TCO has to be good within 6 months or a year. If possible get a modular solution. One where you can replace the parts that are the bottle neck without having to to a fork lift upgrade. That allows for smaller, incremental, affordable improvements until you have either morphed into a new system all together over a period of time or have gotten out of the current solution what’s possible and the time has arrived to replace it. Never would I  invest in an expensive, long term, fork lift, ultra scalable solution. Why not. To expensive and as such to high risk. The risk is due to the fact I don’t have one of these:

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So storage vendors need to perform a delicate balancing act. It’s about price, value, technology evolution, rapid adoption, diversification, integration, assimilation & licensing models in a good enough is good enough world where the solution needs to deliver from day one.

I for one will be very interested if all storage vendors can deliver enough value to retain the mid market or if they’ll become top feeders only. The push to the cloud, the advancements in data replication & protection in the application and platform layer are shaking up the traditional storage world. Combine that with the fast pace at which SSD & Flash storage are evolving together with Windows Server 2012 that has morphed into a very capable storage platform and the landscape looks very volatile for the years to come. Think about  ever more solutions at the application (Exchange, SQL server) and platform layer (Hyper-V replica) with orchestration on premise and/or in the cloud and the pressure is really on.

So how do you choose a solution in this environment?

Whenever you are buying storage the following will happen. Vendors, resellers & sales people, are going to start pulling at you. Now, some are way better than others at this, some are even down right good at this whole process a proceed very intelligently.

Sometimes it involves FUD, doom & gloom combined with predictions of data loss & corruption by what seem to be prophets of disaster. Good thing is when you buy whatever they are selling that day, they can save you from that. The thing is this changes with the profit margin and kickbacks they are getting. Sometimes you can attribute this to the time limited value of technology, things evolve and todays best is not tomorrows best. But some of them are chasing the proverbial $ so hard they portray themselves as untrustworthy fools.

That’s why I’m not to fond of the real big $ projects. Too much politics & sales. Sure you can have people take care of but you are the only one there to look out for your own interests. To do that all you need to do is your own due diligence and be brave. Look, a lot of SAN resellers have never ever run a SAN, servers, Hyper-V clusters, virtualized SQL Server environments or VDI solutions in your real live production environments for a sustained period of time. You have. You are the one whose needs it’s all about as you will have to live and work with the solution for years to come.  We did this exercise and it was worth while. We got the best value for money looking out for our own interests.

Try this with a reseller or vendor. Ask them about how their hardware VSS providers & snapshot software deals with the intricacies of CSV 2.0 in a Hyper-V cluster. Ask them how it works and tell them you need to references to speak to who are running this in production. Also make sure you find your own references. You can, it’s a big world out there and it’s a fun exercise to watch their reactions Winking smile

As Aidan remarked in his blog on ODX–Not All SANs Are Created Equally

These comparisons reaffirm what you should probably know: don’t trust the whitepapers, brochures, or sales-speak from a manufacturer.  Evidently not all features are created equally.

You really have to do your own due diligence. Some companies can afford the time, expense & personnel to have the shortlisted vendors deliver a system for them to test. Costs & effort rise fast if you need to get a setup that’s comparable to the production environment. You need to device tests that mimic real life scenario’s in storage capacity, IOPS, read/write patterns and make sure you don’t have bottleneck outside of the storage system in the lab.

Even for those that can, this is a hard thing to do. Some vendors also offer labs at their Tech Centers or Solutions Centers where customers or potential customers can try out scenarios. No matter what options you have, you’ll realize that this takes a lot of effort. So what do I do? I always start early. You won’t have all the information, question & answers available with a few hours of browsing the internet & reading some brochures. You’ll also notice that’s there’s always something else to deal with or do, so give your self time, but don’t procrastinate. I did visit the Tech Centers & Solution Centers in Europe of short listed vendors. Next to that I did a lot of reading, asked questions and talked to a lot of people about their view and experiences with storage. Don’t just talk to the vendors or resellers. I talked a lot with people in my network, at conferences and in the community. I even tracked down owners of the shortlisted systems and asked to talk to them. All this was part of my litmus test of the offered storage solutions. While perfection is not of this world there is a significant difference between vendor’s claims and the reality in the field. Our goal was to find the best solution for our needs based on price/value and who’s capabilities & usability & support excellence materialized with the biggest possible majority of customers in the field.

Friendly Advice To Vendors

So while the entire marketing and sales process is important for a vendor I’d like to remind all of them of a simple fact. Delivering what you sell makes for very happy customers who’s simple stories of their experiences with the products will sell it by worth of mouth. Those people can afford to talk about the imperfections & some vNext wishes they have. That’s great as those might be important to you but you’ll be able to see if they are happy with their choice and they’ll tell you why.

DELL PowerEdge VRTX Has Potential Beyond ROBO As a Scale Out File Server Building Block

The PowerEdge VRTX

I went to have a chat with Dell at TechEd 2013 Europe in Madrid. The VRTX was launched during DELL Enterprise Forum early June 2013 this concept packs a punch and I encourage you to go look at the VRTX (pronounced as “Vertex”) in more detail here. It’s a very quite setup which can be hooked up to standard power. Pretty energy efficient when you consider the power of the VRTX. And the entire setup surely packs a lot of punch at an attractive price point.

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It can serve perfectly for Remote Office / Branch Office (ROBO) deployments but has many more use cases as it’s very versatile. In my humble opinion DELL’s latest form factor could be used for some very nice scale out scenarios. It’s near perfect for a Windows Server 2012 Scale Out File Server (SOFS) building block. While smaller ones can be build using 1Gbps the future just needs 10Gbps networking.

10Gbps, RDMA (iWarp, RoCE)

That’s the first thing I missed and the first thing I was told that would arrive very soon. So I’m  very happy with that. With sufficient 10Gbps ports to servers and  iWarp or RoCE RDMA capable NICs (there’s cheap enough compared to ordinary 10Gbps cards not to have to leave that capability out) we have all we need to function as powerful building block for the Scale Out File Server model with Windows Server 2012 (R2) where the CSV network becomes the storage network leveraging redirected IO. For this concept look at this picture from a presentation a year ago. SMB 3.0 Multichannel and RDMA make this possible.

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While then I drew the SOFS building blocks out of R720 7 & MD1200  hardware, the VRTX could fit in there perfectly!

Storage Options

Today DELL uses their implementation of Clustered PCI Raid for shared storage which is supported since Windows Server 2012. This is great. For the moment it’s a non redundant setup but a redundant one is in the works I’m told. Nice, but think positive, redirected IO  (block level) over SMB 3.0 would save our storage IO even today. It would be a very wise and great addition to the capabilities of this building block to add the option & support for Storage Spaces. This would make the Scale Out File Server concept shine with the VRTX.

Why? Well I would give us following benefits in the storage layer and the VHDX format in Hyper-V can take benefits :

  • Deduplication
  • Thin Provisioning
  • Management Delegation
  • UNMAP
  • Write Cache
  • Full benefits of ReFS on storage spaces for data protection
  • Automatic Data Tiering with commodity SSD (ever cheaper & bigger) and SAS disks perhaps even the Near Line ones (less power & cooling, great capacity)
  • Potential for JBOD redundancy

Look at that feature set people, in box, delivered by Windows. Sweet! Combine this with 10Gbps networking and DELL has not only a SOFS building block in their port folio, it also offers significant storage features in this package. I for one would like them to do so and not miss out on this opportunity to offer even more capabilities in an attractive price package. Dell could be the very first OEM to grab this new market opportunity by supporting the scale out approach and out maneuver their competitors

Anything Else?

Combine such a building block as described above with their unmatched logistical force for distribution and support this will be a hit a a prime choice for Windows shops. They already have the 10Gbps networking gear & features (DCB) in the PowerConnect 81XX & Force10 S4810 switches. It could be an unbeatable price / capabilities / feature combo that would sell very well.

If we go for SOFS we might need more storage in a single building block with a 4 node cluster. Extensibility might be nice for this. More not just as in capacity but I need to work out the IOPS the available configurations can give us.