Tag Archives: Nutanix Distributed File System

PART 1 – Problems with RAID and Object Based Storage for data protection

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I regularly get asked to compare the resiliency of traditional centralized storage with converged as well as newer technologies such as hyper-converged.

So this post will discuss the problems with RAID and newer hyper-converged solutions using Object based storage for data protection.

This post will discuss two examples below, with Part 2 discussing Hyper-converged solutions using Distributed File Systems.

1. Traditional RAID

2. Hyper-converged Object Based Storage

Starting with Traditional shared storage, and the most common RAID level in my experience, RAID 5.

The below diagram shows a 3 x 4TB SATA drives in a RAID 5 with a Hot Spare.
3 Disk R5 w Hot Spare NO BG

Now lets look a drive failure scenario. We now have the Hot Spare activate and start rebuilding as shown below.

3 Disk R5 w Hot Spare REBUILDING NO BG

So this all sounds fine, we’ve had a drive failure, and a spare drive has automatically taken its place and started rebuilding the data.

The problem now is that even in this simplified/small example we have 2 drives (or say 200 IOPS of drives) trying to rebuild onto just a single drive. So the maximum rate at which the RAID 5 can restore resiliency is limited to that of a single drive or 100 IOPS.

If this was a 8 disk RAID 5, we would have 7 drives (or 700 IOPS) trying to rebuild again to only a single drive or 100 IOPS.

There are multiple issues with this architecture.

  1. The restoration of resiliency of the entire RAID is constrained by the destination drive, in this case a SATA drive which can sustain less than 100 IOPS
  2. A single subsequent HDD failure within the RAID will cause data loss.
  3. The RAID rebuild is a high impact activity on the storage controllers which can impact all storage
  4. The RAID rebuild is an especially high impact activity on the virtual machines running on the RAID.
  5. The larger the RAID or the capacity drives in the RAID, the longer the rebuild takes and the higher the performance impact and chance of subsequent failures leading to data loss.

Now I’m sure most of you understand this concept, and have felt the pain of a RAID rebuild taking many hours or even days, but with new hyper converged technology this issue is no longer a problem, right?

Wrong!

It entirely depends on how data is recovered in the event of a drive failure. Lets look at an example of an hyper-converged solution using an object store.The below shows a simplified example of a Hyper-converged Object Based Storage with 4 objects represented by Object A,B,C and D in Black, and the 2nd replicated copy of the object represented Object A,B,C and D in Purple.

Note: Each object in the Object Store can be hundreds of GB in size.HyperconvergedObjectStoreNormal

Let’s take a look what happens in a disk failure scenario.

HyperconvergedObjectStoreFailure

From the above diagram we can see a drive has failed on Node 1, which means Object A and Object D’s replica have been lost. The object store will then replicate a copy of Object A to Node 4, and a replica of Object D to Node 2 to restore resiliency.

There are multiple issues with this architecture.

  1. Object based storage can lack granularity as Objects can be 200Gb+.
  2. The restoration of resiliency of any single object is constrained by the source drive or node.
  3. The restoration of resiliency of any single object is also constrained by the destination drive or node.
  4. The restoration of multiple objects (such as Object A & D in the above example) is constrained by the same drive or node which will result in contention and slow the process of restoring resiliency to both objects.
  5. The impact of the recovery is High on virtual machines running on the source and destination nodes.
  6. The recovery of an Object is constrained by the source and destination node per object.
  7. Object stores generally require a witness, which is stored on another node in the cluster. (Not illustrated above)

It should be pointed out, where SSDs are used for a write cache, this can help reduce the impact and speed up recovery in some cases, but where data needs to be recovered from outside of cache, i.e.: A SAS or SATA drive, the fact writes go to SSD makes no difference as the writes are constrained by the read performance.

Summary:

Traditional RAID used by SAN/NAS and newer Hyper-converged Object based storage both suffer similar issue when recovering from drive or node failures which include:

  1. The restoration of resiliency is constrained by the source drive or node
  2. The restoration of resiliency is constrained by the destination drive or node
  3. The restoration is high impact on the desination
  4. The recovery of one object is constrained by the network connectivity between just two nodes.
  5. The impact of the recovery is High on any data (such as virtual machines) running on the RAID or source/destination node/s
  6. The recovery of RAID or an Object is constrained by a single part of the infrastructure being a RAID controller / drive or a single node.

In Part 2, we will look at the Hyper-converged Distributed File Systems.

Example Architectural Decision – VMware DRS automation level for a Nutanix environment

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Problem Statement

What is the most suitable DRS automation level and migration threshold for a vSphere cluster running on Nutanix?

Requirements

1. Ensure optimal performance for Business Critical Applications
2. Minimize complexity where possible

Assumptions

1. Workload types and size are unpredictable and workloads may vary greatly and without notice
2. The solution needs to be as automated as possible without introducing significant risk
3. vSphere 5.0 or later

Constraints

1. 2 x 10GB NICs per ESXi host (Nutanix node)

Motivation

1. Prevent unnecessary vMotion migrations which will impact host & cluster performance
2. Ensure the cluster standard deviation is minimal
3. Reduce administrative overhead of reviewing and approving DRS recommendations
4. Ensure optimal storage performance

Architectural Decision

Use DRS in Fully Automated mode with setting “3” – Apply priority 1,2 and 3 recommendations

Create a DRS “Should run on hosts in group” rule for each Business Critical Applications (BCAs) and configure each BCA to run on a single specified host (ensuring BCA’s are separated or grouped according to workload)

DRS Automation will be Disabled for all Controller VMs (CVMs)

Justification

1. Fully Automated DRS prevents excessive vMotion migrations that do not provide significant compute benefits to cluster balance as the vMotion itself will use cluster & network resources

2. Ensure the Nutanix Distributed File System , specifically the “Curator” component does not need to frequently relocate data between Nutanix nodes (ESXi hosts) direct attached storage to ensure virtual machine/s have local access to data. Doing so would put additional load on the Controller VM (and Curator service), local/remote storage and the network.

2. Ensure cluster remains in a reasonably load balanced state without resource being wasted on load balancing the compute layer to only achieve minimal improvement which may impact the storage/network layer/s.

3. Applying Level 1,2 and 3 recommendations means recommendations that must be followed to satisfy cluster constraints, such as affinity rules and host maintenance will be applied (Level 1) as well as applying recommendations with four or more stars (Level 2) that promise a significant improvement in the cluster’s load balance. In the event significant improvement to the clusters load balance will be achieved, movement of data at the storage layer (via the CVM / Network) can be justified

3. DRS is a low risk, proven technology which has been used in large production environments for many years

4. Setting DRS to manual would be a significant administrative (BAU) overhead and introduce additional risks such as human error and situations where contention may go unnoticed which may impact performance of one or more VMs

5. Setting a more aggressive DRS migration threshold may put an additional load on the cluster which will likely not result in significantly better cluster balance (or VM performance) and could result in significant additional workload for the ESXi hosts (compute layer), the Nutanix Controller VM (CVM) ,network & underlying storage.

6. By using DRS “Should run on this host” rules for Business Critical Applications (BCAs) will ensure consistent performance for these workloads (by keeping VMs on the same ESXi host/Nutanix node where its data is local) without introducing significant complexity or limiting vSphere functionally

Implications

1. In some circumstances the DRS cluster may have a low level of imbalance

2. DRS will not move workloads via vMotion where only a moderate improvement to the cluster will be achieved

3. At times, including after performing updates (via VUM) of ESXi hosts (Nutanix Nodes) the cluster may appear to be unevenly balanced as DRS may calculate minimal benefit from migrations. Setting DRS to “Use Fully automated and Migration threshold 3” for a short period of time following maintenance should result in a more evenly balanced DRS cluster with minimal (short term) increased workload for the Nutanix Controller VM (CVM) , network & underlying storage.

4. DRS rules will need to be created for Business Critical Applications

Alternatives

1.Use Fully automated and Migration threshold 1 – Apply priority 1 recommendations
2.Use Fully automated and Migration threshold 3 – Apply priority 1,2 recommendations
3. Use Fully automated and Migration threshold 4- Apply priority 1,2,3 and 4 recommendations
4.Use Fully automated and Migration threshold 5- Apply priority 1,2,3,4 & 5 recommendations
5. Set DRS to manual and have a VMware administrator assess and apply recommendations
6. Set DRS to “Partially automated”

Related Articles

1. Storage DRS and Nutanix – To use or not to use, That is the question

An exciting new adventure for this VCDX

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I am very pleased to announce that I have decided to take on a new challenge and will be joining the innovative team at Nutanix starting July this year in the Solutions and Performance engineering team.

It was only a few short months ago when I first discovered what Nutanix was all about, after previously seeing the classic “No SAN” advertisements on various blogs and at VMworld in 2012, and embarrassingly I have to admit I did not make the time to look into the solution.

Since then, I have spent a lot of time looking into the Nutanix solution and have spoken to a number of people in the industry including several members of the Nutanix family. It has become obvious to me why Nutanix is one of the most successful and fastest growing start-ups in the industry, although im not sure I’d call Nutanix a “Start-up” any more.

The linearly scale out solution provided by Nutanix aligns perfectly with the virtualization best practices that most of us have known for many years, and combines PCIe SSD (Fusion-io) with SATA SSDs and high capacity SATA drives into a high performance , hyper-converged 2RU platform.

Over my many years in the industry I can recall countless scenarios where the Nutanix solution would have been a perfect fit, and solved numerous problems, both at the technical/architectural level and importantly at the business level for both SMB and Enterprise customers.

Now with the release of a wider range of Nutanix blocks including the NX-1000 and NX-6000, the solution is becoming more and more attractive.

In my role I will be part of the team who is responsible for creating high performance solutions and developing best practice guides, reference architectures and case studies for things like virtualization of business critical applications on the Nutanix platform.

A lot of people are already aware of how good the platform is for virtual desktops, but I am not only focused on showing how good the solution is for VDI, but for a wider range of workloads, including Business Critical Applications / server and Big Data workloads.

I am very much looking forward to being a significant part of this exciting company, which already boasts exceptional talent, including two VCDXs in Jason Langone @langonej & Lane Leverett @wolfbrthr . So I am very pleased to be working along side such talent and to be the third VCDX in the Nutanix family.

As I have been doing for the last year or so, I intend to continue to share my experience with the virtualization community via Twitter, Blogging, VMUGs etc, which will now include (but not be limited too) the Nutanix platform.

So stay tuned as the Nutanix team and I have a number of very interesting projects coming up in the next few weeks and months which I cant wait to share with you.

If your not already familiar with what Nutanix is all about, here are a couple of quick introductory YouTube videos which I highly recommend you take the time to watch (as I wish I had sooner!)

About Nutanix | How Nutanix Works | 8 Strategies for a Modern Datacenter

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