Tag Archives: data

Nutanix – Erasure Coding (EC-X) Deep Dive

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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)

Scale Out Shared Nothing Architecture Resiliency by Nutanix

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At VMware vForum Sydney this week I presented “Taking vSphere to the next level with converged infrastructure”.

Firstly, I wanted to thank everyone who attended the session, it was a great turnout and during the Q&A there were a ton of great questions.

I got a lot of feedback at the session and when meeting people at vForum about how the Nutanix scale out shared nothing architecture tolerates failures.

I thought I would summarize this capability as I believe its quite impressive and should put everyone’s mind at ease when moving to this kind of architecture.

So lets take a look at a 5 node Nutanix cluster, and for this example, we have one running VM. The VM has all its data locally, represented by the “A” , “B” and “C” and this data is also distributed across the Nutanix cluster to provide data protection / resiliency etc.

Nutanix5NodeCluster

So, what happens when an ESXi host failure, which results in the Nutanix Controller VM (CVM) going offline and the storage which is locally connected to the Nutanix CVM being unavailable?

Firstly, VMware HA restarts the VM onto another ESXi host in the vSphere Cluster and it runs as normal, accessing data both locally where it is available (in this case, the “A” data is local) and remotely (if required) to get data “B” and “C”.

Nutanix5nodecluster1failed

Secondly, when data which is not local (in this example “B” and “C”) is accessed via other Nutanix CVMs in the cluster, it will be “localized” onto the host where the VM resides for faster future access.

It is importaint to note, if data which is not local is not accessed by the VM, it will remain remote, as there is no benefit in relocating it and this reduces the workload on the network and cluster.

The end result is the VM restarts the same as it would using traditional storage, then the Nutanix cluster “curator” detects if any data only has one copy, and replicates the required data throughout the cluster to ensure full resiliency.

The cluster will then look like a fully functioning 4 node cluster as show below.

5NodeCluster1FailedRebuild

The process of repairing the cluster from a failure is commonly incorrectly compared to a RAID pack rebuild. With a raid rebuild, a small number of disks, say 8, are under heavy load re striping data across a hot spare or a replacement drive. During this time the performance of everything on the RAID pack is significantly impacted.

With Nutanix, the data is distributed across the entire cluster, which even with a 5 node cluster will be at least 20 SATA drives, but with all data being written to SSD then sequentially offloaded to SATA.

The impact of this process is much less than a RAID rebuild as all Nutanix controllers in the cluster participate and take a portion of the workload as a result the impact per disk, per controller ,per node and importantly for production VMs running in the cluster, is greatly reduced.

Essentially, the larger the cluster, the faster the cluster can repair itself, and the lower the impact on production workloads.

Now lets talk about a subsequent ESXi host failure, now we have two failed nodes, and three surviving nodes, and only one copy of data “A” , “B” and “C” as shown below.

Nutanix5NodeCluster2failures1copydata

Now the Nutanix “Curator” detects only one copy of data “A”, “B” and “C” exists and starts to replicate copies of “A”, “B” and “C” across the cluster. This results in the below which is a fully functional and redundant cluster, capable of surviving yet another failure as shown below.

Nutanix5NodeCluster2Failures

Even in this scenario, where two ESXi hosts are lost, the environment still has 60% of its storage controllers (and performance), as compared to a typical traditional storage product where the loss of just two (2) controllers can have your environment completely offline, and even if you only lost a single controller, you would only have 50% of the storage controllers (and performance) available.

I think this really highlights what VMware and players like Google, Facebook & Twitter have been saying for a long time, scaling out not up, and shared nothing architecture is the way of the future. The only question is who will be dominant in bringing this technology to the mass market, and I think you know who I have my money on.

Data Centre Migration Strategies – Part 2 – Lift and Shift

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Continuing on from Data Centre Migration Strategies Part 1 – Overview, Part 2 focuses on the “Lift and Shift” method.

I’m sure your reading this and already thinking, “this is the least interesting migration strategy, tell me about vMSC and SRM!” and well, your right, BUT it is important to understand the pros and cons so if you are ever in a situation where you have to use this method (I have on numerous occasions) that the migration is successful.

So what are the pros and cons of this method.

Pros

1. No need to purchase equipment for the new data centre
2. The environment should perform as it did at the original data centre following relocation
3.The approach is simple from a technical perspective ie: No new products are required
4. Low direct cost (Note: Point 8 in Cons)
5. Achieves a Recovery Point Objective (RPO) of zero (0).

Cons

1. The entire environment needs to be fully shut-down
2. The outage for the environment starts from when the servers are shut-down, until completion of operational verification testing at the new datacenter. Note: This may take several days depending on the size of the environment.
3. This method is high risk as the ability to fail back to the original datacenter requires all equipment be physically relocated back. This means the Recovery Time Objective (RTO) cannot be low.
4. The Lift and shift method cannot be tested until at least a significant amount of equipment has been physical relocated
5. In the event of an issue during operational verification at the new data centre, a decision needs to be made to proceed and troubleshoot the issues, OR at what point to fail back.
6. Depending on your environment, a vendor (eg: Storage) may need to revalidate your environment
7. Your migration (and schedule) are heavily dependant on the logistical side of the relocation which may have many factors (eg: Traffic / Weather) which are outside your control which may lead to delays or failed migration.
8. Potentially high indirect cost eg: Downtime, Loss of Business , productivity etc

When to use this method?

1. When purchasing equipment for the new data centre is not possible
2. When extended outages to the environment are acceptable
3. When you have no other options

Recommendations when using “Lift and Shift”

1. Ensure you have accurate wiring and rack diagrams of your datacenter
2. Be prepared with your vendor support contact details on hand as it is common following relocation of equipment to have hardware failures
3. Ensure you have an accurate Operational Verification document which tests every part of your environment from Layer 1 (Physical) all the way to Layer 7 (Application)
4. Label EVERYTHING as you disconnect it at the original datacenter
5. Prior to starting your data centre  migration, discuss and agree on a timeline for the migration and at what point and under what situation do you initiate a fail back.
6. Migrate the minimum amount of physical equipment that is required to get your environment back on-line and do your Operational Verification, then on successful completion of your Operational Verification migrate the remaining equipment. This allows for faster fail-back in the event Operational Verification fails.

In Part 3, we discuss Data centre migrations using VMware Site Recovery Manager. (Coming soon)