Deduplication and MS Exchange

Virtualization and Storage always seem to be a hot topics in regards to Exchange deployments and many of you would have seen my post Virtualizing Exchange on vSphere with NFS backed storage a while back.

This post was motivated by a tweet from fellow VCDX which stated:

dedupe not supported for Exchange, no we can’t turn it off.

Later in the twitter conversation he went on to say

To be clear not an MS employee, another integrator MS “master” certified. It’s the whole NFS thing again

I have heard similar over the years and for me the disappointing thing is the support statement is unclear as are the motivations behind support statements for Exchange in general. e.g.: Support for VMDK on NFS

The only support statement I am aware of regarding Exchange and deduplication is in the technet article “Exchange 2013 storage configuration options” under the section “Volume configurations for the Exchange 2013 Mailbox server role” at it states:

storageexchange

In the above statement which specifically refers to “a new technique to optimize storage utilization for Windows Server 2012” is states that for Stand-alone or High availability solutions de-duplication is not supported for Exchange database file unless the DB files are completely offline and used for backup or archives.

So the first question is “Is array level deduplication supported”?

There is nothing that says that it isn’t supported that I am aware of, so if you are aware of such a statement please let me know in the comments and I will update this post.

My interpretation of the support statement is that array level deduplication is supported and MS have simply called out that the deduplication in Windows 2012 is not. Regardless of if you agree or disagree with my interpretation, I think its safe to say the support statement should be clarified with justification.

The next question I would like to discuss is “Should deduplication be used with Exchange”?

Firstly we should discuss the fact Exchange can be deployed with Database Availability Groups (DAGs) which creates multiple copies of Exchange databases across up to 16 Exchange Mailbox (or Multi-Role) servers.

The purpose of a DAG is to provide high availability for the application and data.

So if the application is by design making duplicate copies, should the storage be undoing this work?

Before I give my opinion on deduplicating DAG copies, I want to be clear on two things:

1. Deduplication is a well proven technology which many different vendors implement either in-line or post process or in some cases both.

2. As array level deduplication is abstracted from the Guest OS and Application, there is no risk to the application such as data corruption or anything like that.

So back to deduplicating DAG copies.

I work for Nutanix and I wrote our best practice guide for Exchange which can be found below. In the guide, I recommended Compression but not deduplication. In an upcoming update of the document the recommendation remains to use compression but adds a further recommendation to use Erasure coding (EC-X) for data reduction.

Nutanix Best Practices Guide: Virtualizing Microsoft Exchange on Web-Scale Converged Infrastructure.

The reason for these recommendations is three fold:

1. Compression + EC-X give excellent data reduction savings for Exchange which generally result in usable capacity higher than RAW capacity while still providing data protection at the storage layer.

2. Deduplicating data which is deliberately written multiple times is a huge overhead on any infrastructure as data is still processed multiple times by the Guest OS, Storage Network and storage controller even if deplicate copies are not written to disk. To be clear, the Guest OS (CPU) and Storage network overhead are not eliminated by dedupe.

3. Nutanix recommends the use of hybrid nodes for Exchange with a small percentage of capacity provided by SSD (for all write I/O and hot data) and a large percentage of capacity provided by SATA. As a result the bulk of the data is stored on low cost SATA so the commercial benefit ($ per GB) of deduplication is minimal especially after compression and EC-X.

In my opinion deduplicating everything regardless of its profile is not the answer, so data reduction such as deduplication, compression and Erasure Coding should be able to be turned off for workloads which give minimal benefit.

For Exchange DAGs, deduplication should give excellent data reduction results in line with the number of DAG copies. So if an Exchange DAG has 4 copies, then approx 4:1 data reduction should be achieved right off the bat. Now this sounds great but when running a DAG on highly available shared storage (SAN/NAS/HCI) it is unnessasary to have 4 copies of data.

In reality, I recommend 2 copies when running on Nutanix because the shared storage provided by Nutanix keeps at least 1 additional copy (if using EC-X) or where using RF2 or RF3, 2 or 3 copies of data meaning in the event of a drive or node failure, the data is still available to the application without requiring a DAG failover. Similar is true when running Exchange on SAN/NAS/HCI solutions with some form of RAID or replication for data protection.

So the benefit of deduplication would therefore reduce to from possibly 4:1 down to 2:1 because only 2 DAG copies are really required if the storage is highly available.

Considering the data reduction from compression and storage solutions supporting Erasure Coding, I think deduplication is only commercially viable/required when using expensive all flash storage which lets face it, is not required for Exchange.

If you have chosen an all flash solution and you want to run all workloads on it and eliminate having silos of infrastructure for different workloads, then by all means deduplicate Exchange DAGs otherwise it will be a super expensive solution. But, in my opinion hybrid is still the best solution overall with the only real advantage of all flash being potentially higher and more consistent performance depending on many factors.

Summary:

I hope that Microsoft clarify their position regarding support for array level data reduction technologies including deduplication with detailed justifications.

I would be disappointed to see Microsoft come out and update the support policy stating deduplication (for array’s) is not supported as there is not technical reason it should not be supported (Happy to be corrected if credible evidence can be provided) regardless of if you think its a good idea or not.

Having worked in the storage industry for a long time, I have seen many different deduplication solutions used successfully with MS Exchange and I am yet to see any evidence that it is not a totally viable and enterprise grade option for Exchange databases.

The question which remains is, do you need to deduplicate Exchange databases? – My thinking is only where your using all flash systems and need to lower cost per GB.

My position being the better solution would be choose a hybrid solution when eliminating silos which gives you the best of all worlds and applications requiring all flash can have all flash and other workloads can use flash for hot data and lower cost SATA for cold storage or data which doesn’t require SSD (like Exchange).

Nutanix – Erasure Coding (EC-X) Deep Dive

I published a post earlier this month during the .NEXT conference titled “What’s .NEXT? – Erasure Coding!” which covered the basics of Nutanix EC-X implementation.

This post is a deep drive follow on to answer numerous questions I have received about EC-X such as:

1. Does it work with Compression and De-duplication?
2. Can I use EC-X to reduce the overhead of RF3?
3. Does it work on Hot or Cold data?
4. Does it work only on the SATA tier?
5. What is the performance impact?
6. When should I use/not use EC-X?
7. What’s different about Nutanix (Patent pending) EC-X compared to other EC algorithms?
8. How does EC-X impact Data Locality?
9. What Hypervisors is EC-X supported with?

So let’s start with What’s different about Nutanix (Patent pending) EC-X compared to other EC algorithms?

* Nutanix EC-X is optimized for a distributed platform, where data is spread across nodes, not individual disks to ensure optimal performance. This also ensures rebuild times are faster and lower impact as the rebuild is performed across all the nodes/drives.

* Nutanix EC-X is also performed as a background task and only on Write Cold data meaning the configured RF is completed as normal and then as a post process EC-X is performed to ensure the write process is not potentially slowed by requiring numerous nodes within the cluster to participate in the initial write I/O.

How does EC-X affect existing Nutanix Data Reduction technologies.

* Short answer, EC-X is complimentary to both compression and deduplication so you will get even more data reduction. Here is a sample screen shot from the Home screen in PRISM which shows a breakdown of Dedup, Compression and Erasure Coding savings.

CapacityOptimization

In the Storage Tab within PRISM, we can get further details on the capacity savings. Here we see an example Container with Compression and EC-X enabled:

CompplusECXhighlighted

Does it work only on the SATA tier?

No, EC-X works on all tiers, being SSD and SATA today, but in the future when newer technology or more than two tiers are used, EC-X works across all tiers.

Does EC-X work on Hot or Cold data?

EC-X waits until data written (via RF2 or RF3) is “Write Cold”, meaning the data is not being overwritten. The data might be white hot from a read I/O perspective, but as long as its not being overwritten the extent group (4MB) will be a candidate for EC-X.

This means for data which is Write Cold, the effective capacity of the SSD tier will be increased due to requiring less space thanks to EC-X.

What is the performance impact?

As EC-X is a post process task and EC-X waits until data is “Write Cold” before performing EC-X on the data, in general it will not impact the Write performance.

The exception to this is in the event data is Write Cold for a period of time, then the data is overwritten, this “overwrite” will incur a higher penalty than a typical RF2/RF3 write. As such some workloads may not be suitable for EC-X which I will discuss later.

Overall, if the workload is suitable, EC-X will keep the data in the SSD tier and the parity on the SATA tier which effectively extends the usable capacity of the SSD tier therefore helping to increase performance (as with compression and dedup).

What Hypervisors is EC-X supported with?

Everything in the Nutanix Distributed Storage Fabric (part of the Nutanix Xtreme Computing Platform or XCP) is designed to be hypervisor agnostic. So whatever Hypervisor/s you choose, you can benefit from EC-X!

How does EC-X impact Data Locality?

As the initial Write path is not impacted by enabling EC-X, Data Locality is still maintained and ensures one copy of data is written to the local node where the VM is running while replicating a further one or two copies (dependent on RF configuration) throughout the cluster.

This means that for newly written data as well as data being overwritten at frequencies of <60mins will always maintain data locality.

For data which meets the criteria for EC-X to be performed, such as Read Hot or Write Cold data, Data Locality can only be partially maintained as the data is by design striped across nodes. The result of this means that it is probable Read I/O will be performed over the network.

Importantly though Read Hot data will be maintained in the SSD tier and be distributed throughout the cluster. This means a single VMs read I/O can be served by multiple nodes concurrently which can lead to increased performance.

As EC-X also provides capacity savings, this allows for more data to be serviced by the SSD tier which enabled a larger active working set to perform at SSD speeds.

In summary, while Data Locality is not always maintained when using EC-X, the advantages of EC-X far outweigh the partial loss in Data Locality.

And finally, When should I use/not use EC-X?

As discussed earlier, EC-X is applied to Write Cold data and if/when that data is overwritten, the write penalty is higher than a typical RF2 write I/O. So if your dataset has a high percentage of overwrites, it is recommended not to use EC-X. The good news is storage can be assigned on a per VMDK level (or vDisk at the NDFS layer) so you can have one VM using EC-X for some data and RF2/3 for other data, again giving customers the best of both worlds.

The best workloads for EC-X are:

1. File Servers
2. Backup
3. Archive
4. Email
5. Logging

Summary:

Nutanix EC-X gives customers more choice without compromising functionality and performance while dramatically reduces the cost/GB of storage.

Related Articles:

  1. Large scale clusters and increased resiliency with RF3 + EC-X
  2. What I/O will Nutanix Erasure coding (EC-X) take effect on?

  3. Sizing assumptions for solutions with Erasure Coding (EC-X)

Deduplication ratios – What should be included in the reported ratio?

I saw the below picture posted on Twitter, and there has been some discussion around the de-duplication ratio (shown below as an an amazing 28.4:1) and what this should and should not include.

03-Jan-15 12-39-25 PMA

In the above case, this ratio includes VM snapshots or what some people in my opinion incorrectly refer to as “backups” (But that’s a topic for another post). In other storage solutions, things like savings from intelligent cloning may also be included.

First l’d like to briefly explain what de-duplication means to me.

I think the below diagram really sums it up well. If 12 pieces of data exist (ie: Have been written or are in the process of being written in the case of in-line de-duplication) to the storage layer, de-duplication (in-line or post process) removes the duplicate data and uses pointers to direct duplicates back to a single copy rather than storing duplicates.

deduplication_diagram

The above image is courtesy of www.enterprisestorageguide.com.

In the above example, the original data has 12 blocks which have been de-duplicated down to 4 blocks.

With this in mind, what should be included in the de-duplication ratio?

The following are some ways to reduce data consumption which in my opinion add value to a storage solution:

1. De-duplication (In-line or post process)
2. Intelligent cloning i.e.: Things like VAAI-NAS Fast File Clone, VCAI, FlexClone etc
3. Point in time snapshot recovery points. (As they are not backups until stored elsewhere)

Obviously, if data that exists or is being written to a storage system and its de-duplicated in-line or post process, this data reduction should be included in the ratio. I’d be more than a little surprised if anyone disagreed on this point.

The one exception to this is where VMDKs are Eager Zeroed Thick (EZT) and de-duplication is simply removing 0’s which in my opinion is simply putting additional load on the storage controllers and over inflating the de-duplication ratio when thin provisioning can be used.

For storage solutions de-duplicating zeros from EZT VMDKs, these capacity savings should be called out as a separate line item. (Discussed later in this post).

What about Intelligent cloning? Well the whole point of intelligent cloning is not to write or have the storage controllers process duplicate data in the first place. So based on this, VMs which are intelligently cloned are not deduped as duplicate data is never written or processed.

As such its my opinion Intelligent cloning savings should not be included in the de-duplication ratio.

Next lets talk “point in time snapshot recovery points“.

The below image shows the VM before a snapshot (a.) has blocks A,B,C & D.

Then after a snapshot without modifications, the VM has the same blocks A,B,C & D.

Then finally, when the VM makes modifications to or deletes data after the snapshot, we see the A,B,C & D remain in tact thanks to the snapshot but then we have a deleted item (B) then modified data (D+) along with net new data E1 & E2.

Feature-Snapshots-Full

Image courtesy of www.softnas.com.

So savings from snapshots are also not “de-duplicating” data, they are simply preventing new data being written, much like intelligent cloning.

As with Intelligent cloning savings, my opinion is savings from snapshots should not be included in the de-duplication ratio.

Summary

In my opinion, the de-duplication ratio reported by a storage solution should only include data which has been written to disk (post process), or was in the process of being written to disk (in-line) that has been de-duplicated.

But wait there’s more!

While I don’t think capacity savings from Intelligent cloning and snapshots should be listed in the de-duplication ratio, I think these features are valuable and the benefits of these technologies should be reported.

I would suggest a separate ratio be reported, for example, Data Reduction.

The Data reduction ratio could report something like the following where all capacity savings are broken out to show where the savings come from:

1) Savings from Deduplication: 2.5:1 (250GB)
2) Savings from Compression: 3:1 (300GB)
3) Savings from Intelligent Cloning: 20:1 (2TB)
4) Savings from Thin Provisioning: 50:1 (5TB)
5) Savings from Point in time Snapshots: 30:1 (3TB)
6) Savings from removal of zeros in EZT VMDKs: 100:1 (10TB)

Then the Total data reduction could be listed e.g.: 60.5:1 (20.7TB)

For storage solutions, the effective capacity of each storage tiers (Memory/SSD/HDD) for example could also be reported as a result of the data reduction savings.

This would allow customers to compare Vendor X with Vendor Y’s deduplication or compression benefits, or compare a solution which can intelligently clone with one that cannot.

Conclusion: 

The value of deduplication, point in time snapshots and intelligent cloning in my mind are not in question, and I would welcome a discussion with anyone who disagrees.

I’d hate to see a customer buy product “X” because it was advertised to have a 28.4:1 dedupe ratio and then find they only get 2:1 because they don’t for example take 4 hourly snapshots of every VM in the environment.

The point here is to educate the market on what capacity savings are achieved and how so customers can compare apples with applies when making purchasing decisions for datacenter infrastructure.

As always, feedback is welcomed.

*Now I’m off to check what Nutanix reports as de-duplication savings. 🙂