Microsoft Software Defined Storage AKA Scale-out File Server (SOFS)

Business Challenges:

  • $/IOPS and $/TB
  • Continuous Availability
  • Fault Tolerance
  • Storage Performance
  • Segregation of production, development and disaster recovery storage
  • De-duplication of unstructured data
  • Segregation of data between production site and disaster recovery site
  • Continuous break fix of Distributed File Systems (DFS) & File Server
  • Continuously extending storage on the DFS servers
  • Single point of failure
  • File systems is not available always
  • Security of file systems is constant concern
  • Propitiatory non-scalable storage
  • Management of physical storage
  • Vendor lock-in contract for physical storage
  • Migration path from single vendor to multi vendor storage provider
  • Management overhead of unstructured data
  • Comprehensive management of storage platform


Microsoft Software Defined Storage AKA Scale-Out File Server is a feature that is designed to provide scale-out file shares that are continuously available for file-based server application storage. Scale-out file shares provides the ability to share the same folder from multiple nodes of the same cluster.Microsoft Software Defined Storage offerings compared with third party offering:

Storage feature Third-party NAS/SAN Microsoft Software-Defined Storage
Fabric Block protocol


File protocol Network


Network Low latency network with FC


Low latency with SMB3Direct Management


Management Management of LUNs


Management of file shares Data de-duplication


Data De-duplication Data de-duplication


Data de-duplication Resiliency


Resiliency RAID resiliency groups


Flexible resiliency options Pooling


Pooling Pooling of disks


Pooling of disks Availability


Availability High


Continuous (via redundancy) Copy offload, Snapshots


Copy Offloads, Snapshots Copy offload, Snapshots


SMB copy offload, Snapshots Tiering


Tiering Storage tiering


Performance with tiering Persistent write-back cache


Persistent Write-back cache Persistent write-back cache


Persistent write-back cache Scale up


Scale up Scale up


Automatic scale-out rebalancing Storage Quality of Service (QoS)


Storage Quality of Service (QoS) Storage QoS


Storage QoS (Windows Server 2016) Replication


Replication Replication


Storage Replica (Windows Server 2016) Updates


Updates Firmware updates


Rolling cluster upgrades (Windows Server 2016)


    Storage Spaces Direct (Windows Server 2016)


    Azure-consistent storage (Windows Server 2016)


 Functional use of Microsoft Scale-Out File Servers:

1. Application Workloads

  • Microsoft Hyper-v Cluster
  • Microsoft SQL Server Cluster
  • Microsoft SharePoint
  • Microsoft Exchange Server
  • Microsoft Dynamics
  • Microsoft System Center DPM Storage Target
  • Veeam Backup Repository

2. Disaster Recovery Solution

  • Backup Target
  • Object storage
  • Encrypted storage target
  • Hyper-v Replica
  • System Center DPM

3. Unstructured Data

  • Continuously Available File Shares
  • DFS Namespace folder target server
  • Microsoft Data de-duplication
  • Roaming user Profiles
  • Home Directories
  • Citrix User Profiles
  • Outlook Cached location for Citrix XenApp Session Server

4. Management

  • Single Management Point for all Scale-out File Servers
  • Provide wizard driven tools for storage related tasks
  • Integrated with Microsoft System Center

Business Values:

  • Scalability
  • Load balancing
  • Fault tolerance
  • Ease of installation
  • Ease of management/operations
  • Flexibility
  • Security
  • High performance
  • Compliance & Certification

SOFS Architecture:

Microsoft Scale-out File Server (SOFS) is  considered as a Storage Defined Storage (SDS).  Microsoft SOFS is independent of hardware vendor as long as the compute and storage is certified by Microsoft Corporation. The following figure shows Microsoft Hyper-v cluster, SQL Cluster and Object Storage on the SOFS.


                 Figure: Microsoft Software Defined Storage (SDS) Architecture


                     Figure: Microsoft Scale-out File Server (SOFS) Architecture


                                      Figure: Microsoft SDS Components


                        Figure: Unified Storage Management (See Reference)

Microsoft Software Defined Storage AKA Scale-out File Server Benefits:


  • Continuous availability file stores for Hyper-V and SQL Server
  • Load-balanced IO across all nodes
  • Distributed access across all nodes
  • VSS support
  • Transparent failover and client redirection
  • Continuous availability at a share level versus a server level


  • Identifies duplicate chunks of data and only stores one copy
  • Provides up to 90% reduction in storage required for OS VHD files
  • Reduces CPU and Memory pressure
  • Offers excellent reliability and integrity
  • Outperforms Single Instance Storage (SIS) or NTFS compression.

SMB Multichannel

  • Automatic detection of SMB Multi-Path networks
  • Resilience against path failures
  • Transparent failover with recovery
  • Improved throughput
  • Automatic configuration with little administrative overhead

SMB Direct:

  • The Microsoft implementation of RDMA.
  • The ability to direct data transfers from a storage location to an application.
  • Higher performance and lower latency through CPU offloading
  • High-speed network utilization (including InfiniBand and iWARP)
  • Remote storage at the speed of local storage
  • A transfer rate of approximately 50Gbps on a single NIC port
  • Compatibility with SMB Multichannel for load balancing and failover

VHDX Virtual Disk:

  • Online VHDX Resize
  • Storage QoS (Quality of Service)

Live Migration

  • Easy migration of virtual machine into a cluster while the virtual machine is running
  • Improved virtual machine mobility
  • Flexible placement of virtual machine storage based on demand
  • Migration of virtual machine storage to shared storage without downtime

Storage Protocol:

  • SAN discovery (FCP, SAS, iSCSI i.e. EMC VNX, EMC VMAX)
  • NAS discovery (Self-contained NAS, NAS Head i.e. NetApp OnTap)
  • File Server Discovery (Microsoft Scale-Out File Server, Unified Storage)

Unified Management:

  • A new architecture provides ~10x faster disk/partition enumeration operations
  • Remote and cluster-awareness capabilities
  • SM-API exposes new Windows Server 2012 R2 features (Tiering, Write-back cache, and so on)
  • SM-API features added to System Center VMM
  • End-to-end storage high availability space provisioning in minutes in VMM console
  • More Windows PowerShell


  • More resilience to power failures
  • Highest levels of system availability
  • Larger volumes with better durability
  • Scalable to petabyte size volumes

Storage Replica:

  • Hardware agnostic storage configuration
  • Provide a DR solution for planned and unplanned outages of mission critical workloads.
  • Use SMB3 transport with proven reliability, scalability, and performance.
  • Stretched failover clusters within metropolitan distances.
  • Manage end to end storage and clustering for Hyper-V, Storage Replica, Storage Spaces, Scale-Out File Server, SMB3, Deduplication, and ReFS/NTFS using Microsoft software
  • Reduce downtime, and increase reliability and productivity intrinsic to Windows.

Cloud Integration:

  • Cloud-based storage service for online backups
  • Windows PowerShell instrumented
  • Simple, reliable Disaster Recovery solution for applications and data
  • Supports System Center 2012 R2 DPM

Implementing Scale-out File Server

Scale-out File Server Recommended Configuration:

  1. Gather all virtual servers IOPS requirements*
  2. Gather Applications IOPS requirements
  3. Total IOPS of all applications & Virtual machines must be less than available IOPS of physical storage 
  4. Keep latency below 3 ms at all time for high performance
  5. Gather required capacity + potential growth + best practice
  6. N+1 Compute, Network and Storage Hardware
  7. Use low latency, high throughput networks
  8. Segregate storage network from data network using logical network (VLAN) or fibre channel
  9. Tools to be used

*Not all virtual servers are same, DHCP server generate few IOPS, SQL server and Exchange can generate thousands of IOPS.

*Do not place SQL Server on the same logical volume (LUN) with Exchange Server or Microsoft Dynamics or Backup Server.

*Isolate high IO workloads to separate logical volume or even separate storage pool if possible.

Prerequisites for Scale-Out File Server

  1. Install File and Storage Services server role, and the Failover Clustering feature on the cluster nodes
  2. Configure Microsoft failover Clusters using this article Windows Server 2012: Failover Clustering Deep Dive Part II
  3. Add Cluster Share Volume
  • Log on to the server as a member of the local Administrators group.
  • Open Server Manager> Click Tools, and then click Failover Cluster Manager.
  • Click Storage, right-click the disk that you want to add to the cluster shared volume, and then click Add to Cluster Shared Volumes> Add Storage Presented to this cluster.

Configure Scale-out File Server

  1. Open Failover Cluster Manager> Right-click the name of the cluster, and then click Configure Role.
  2. On the Before You Begin page, click Next.
  3. On the Select Role page, click File Server, and then click Next.
  4. On the File Server Type page, select the Scale-Out File Server for application data option, and then click Next.
  5. On the Client Access Point page, in the Name box, type a NETBIOS of Scale-Out File Server, and then click Next.
  6. On the Confirmation page, confirm your settings, and then click Next.
  7. On the Summary page, click Finish.

Create Continuously Available File Share

  1. Open Failover Cluster Manager>Expand the cluster, and then click Roles.
  2. Right-click the file server role, and then click Add File Share.
  3. On the Select the profile for this share page, click SMB Share – Applications, and then click Next.
  4. On the Select the server and path for this share page, click the name of the cluster shared volume, and then click Next.
  5. On the Specify share name page, in the Share name box, type a name for the file share, and then click Next.
  6. On the Configure share settings page, ensure that the Continuously Available check box is selected, and then click Next.
  7. On the Specify permissions to control access page, click Customize permissions, grant the following permissions, and then click Next:
  • To use Scale-Out File Server file share for Hyper-V: All Hyper-V computer accounts, the SYSTEM account, cluster computer account for any Hyper-V clusters, and all Hyper-V administrators must be granted full control on the share and the file system.
  • To use Scale-Out File Server on Microsoft SQL Server: The SQL Server service account must be granted full control on the share and the file system

      8. On the Confirm selections page, click Create. On the View results page, click Close.

Use SOFS for Hyper-v Server VHDX Store:

  1. Open Hyper-V Manager. Click Start, and then click Hyper-V Manager.
  2. Open Hyper-v Settings> Virtual Hard Disks> Specify Location of Store as \\SOFS\VHDShare\ and Specify location of Virtual Machine Configuration \\SOFS\VHDCShare
  3. Click Ok.

Use SOFS in System Center VMM: 

  1. Add Windows File Server in VMM
  2. Assign SOFS Share to Fabric & Hosts

Use SOFS for SQL Database Store:

1. Assign SQL Service Account Full permission to SOFS Share

  • Open Windows Explorer and navigate to the scale-out file share.
  • Right-click the folder, and then click Properties.
  • Click the Sharing tab, click Advanced Sharing, and then click Permissions.
  • Ensure that the SQL Server service account has full-control permissions.
  • Click OK twice.
  • Click the Security tab. Ensure that the SQL Server service account has full-control permissions.

2. In SQL Server 2012, you can choose to store all database files in a scale-out file share during installation.  

3. On the step 20 of SQL Setup Wizard , provide a location of Scale-out File Server which is \\SOFS\SQLData and \\SOFS\SQLLogs

4. Create a Database on SOFS Share but on the existing SQL Server using SQL Script

( NAME = N’TestDB’, FILENAME = N’\\SOFS\SQLDB\TestDB.mdf’ )
( NAME = N’TestDBLog’, FILENAME = N’\\SOFS\SQLDBLog\TestDBLogs.ldf’)

Use Backup & Recovery:

System Center Data Protection Manager 2012 R2

Configure and add a dedupe storage target into DPM 2012 R2. DPM 2012 R2 will not backup SOFS itself but it will backup VHDX files stored on SOFS. Follow Deduplicate DPM storage and protection for virtual machines with SMB storage  guide to backup virtual machines.

Veeam Availability Suite

  1. Log on to Veeam Availability Console>Click Backup Repository> Right Click New backup Repository
  2. Select Shared Folder on the Type Tab
  3. Add SMB Backup Target \\SOFS\Repository
  4. Follow the Wizard. Make Sure Service Account of Veeam has full access permission to \\SOFS\Repository  Share.
  5. Click Scale-out Repositories>Right Click Add Scale-out backup repository> Type the Name
  6. Select the backup repository you created in previous>Follow the Wizard to complete tasks.


Microsoft Storage Architecture

Storage Spaces Physical Disk Validation Script

Validate Hardware

Deploy Clustered Storage Spaces

Storage Spaces Tiering in Windows Server 2012 R2

SMB Transparent Failover

Cluster Shared Volume (CSV) Inside Out

Storage Spaces – Designing for Performance

Related Articles:

Scale-Out File Server Cluster using Azure VMs

Microsoft Multi-Site Failover Cluster for DR & Business Continuity

Understanding Software Defined Storage (SDS)

Software defined storage is an evolution of storage technology in cloud era. It is a deployment of storage technology without any dependencies on storage hardware. Software defined storage (SDS) eliminates all traditional aspect of storage such as managing storage policy, security, provisioning, upgrading and scaling of storage without the headache of hardware layer. Software defined storage (SDS) is completely software based product instead of hardware based product. A software defined storage must have the following characteristics.

Characteristics of SDS

  • Management of complete stack of storage using software
  • Automation-policy driven storage provisioning with SLA
  • Ability to run private, public or hybrid cloud platform
  • Creation of uses metric and billing in control panel
  • Logical storage services and capabilities eliminating dependence on the underlying physical storage systems
  • Creation of logical storage pool
  • Creation of logical tiering of storage volumes
  • Aggregate various physical storage into one or multiple logical pool
  • Storage virtualization
  • Thin provisioning of volume from logical pool of storage
  • Scale out storage architecture such as Microsoft Scale out File Servers
  • Virtual volumes (vVols), a proposal from VMware for a more transparent mapping between large volumes and the VM disk images within them
  • Parallel NFS (pNFS), a specific implementation which evolved within the NFS
  • OpenStack APIs for storage interaction which have been applied to open-source projects as well as to vendor products.
  • Independent of underlying storage hardware

A software defined storage must not have the following limitations.

  • Glorified hardware which juggle between network and disk e.g. Dell Compellent
  • Dependent systems between hardware and software e.g. Dell Compellent
  • High latency and low IOPS for production VMs
  • Active-passive management controller
  • Repetitive hardware and software maintenance
  • Administrative and management overhead
  • Cost of retaining hardware and software e.g. life cycle management
  • Factory defined limitation e.g. can’t do situation
  • Production downtime for maintenance work e.g. Dell Compellent maintenance

The following vendors provides various software defined storage in current market.

Software Only vendor

  • Atlantis Computing
  • DataCore Software
  • Nexenta
  • Maxta
  • CloudByte
  • VMware
  • Microsoft

Mainstream Storage vendor

  • EMC ViPR
  • HP StoreVirtual
  • Hitachi
  • IBM SmartCloud Virtual Storage Center
  • NetApp Data ONTAP

Storage Appliance vendor

  • Tintri
  • Nimble
  • Solidfire
  • Nutanix
  • Zadara Storage

Hyper Converged Appliance

  • Cisco (Starting price from $59K for Hyperflex systems+1 year support inclusive)
  • Nutanix
  • VCE (Starting price from $60K for RXRAIL systems+support)
  • Simplivity Corporation
  • Maxta
  • Pivot3 Inc.
  • Scale Computing Inc
  • EMC Corporation
  • VMware Inc

Ultimately, SDS should and will provide businesses will worry free management of storage without limitation of hardware. There are compelling use cases of software defined storage for an enterprise to adopt software defined storage.

Relavent Articles

Dell Compellent: A Poor Man’s SAN

I have been deploying Storage Area Network for almost ten years in my 16 years Information Technology career. I have deployed various traditional, software defined and converged SANs manufactured by a global vendor like IBM, EMC, NetApp, HP, Dell, etc. I was tasked with the deployment of Dell Compellent in my previous role for several clients. I was excited about the opportunities and paused after reading the documentation presented to me. I could not co-relate implementation of a SAN and expected outcome desired by clients. When over wild sales pitch is sold to businesses with high promises, then there will always be hidden risks that come with this sales pitch. Lesson number one never trusts someone blindly although they have a very decent track record, resellers are often after a quick sale and get out. Lesson number two make sure you know who to trust as your partner in the transition to have a new SAN. Decide what to procure based on your business case, ROI, workload analysis, capacity planning, lession learnt and outcome of requirement analysis. Consider current technology trend, where you are at now, a technology road map and where you want to be in future, e.g. Google Cloud, AWS or Azure. Capital investment can be the one off exercise these days before you pull the plug off on the on-premises infrastructure and fork-lift to Azure, Amazon or Google Cloud. Consider aligning technology stream with the business you do. I have written this article to share my own experience and disclose everything I learnt through my engagement on Dell Compellent deployment projects so that you can make a call by yourself. I will elaborate each feature of Dell Compellent and what exactly this feature does when you deploy a Compellent. FYI I have no beef with Dell. Let’s start now… “Marketing/sales pitch” vs “practical implication.”

Target Market: Small Business

Lets not go into detail, that will be a different topic for another day. Please read Dell’s business proposition “Ideally suited to smaller deployments across a variety of workloads, the SC Series products are easy to use and value optimized. We will continue to optimize the SC Series for value and server-attach.”

Management Interface: Dell Compellent Storage Center has a GUI designed to be accessible allegedly ease of use. Wizards offer few everyday tasks such as allocation, configuration, and administration functions. Compellent Storage Center monitoring tools provide very little insight on how storage backend is doing. You have to engage Dell remote support for diagnostic, and monitoring tools with alert and notification services. Storage center is not as granular as the competitor NetApp and EMC. Storage center has little information on storage performance, bottle neck and backend storage issues. Compellent is by design thin provisioned storage. There is no option in management center to assign as thick provisioned volume. IOPS and latency are calculated in volume and IOPS and latency are calculated in disks are far too different than real IOPS. You may see little IOPS in volume but click at drive level IOPS you will see storage controller is struggling to cope with the IOPS. Management center does not provide any clues who is generating this much IOPS.

Contact technical support they will say RAID scrub is killing your storage. Your standard request to tech support that stops the RAID scrub in a business hour. “You cannot do it” another classic reply by tech support. If you go through Compellent management center, you will find nothing that can schedule or stop RAID scrub.

Data Progression: In theory, Data Progression is an automated tiering technology that should have optimised the location of data, both on a schedule and on demand as prompted by a storage profile. Compellent’s tiering profiles streamline policy administration by assigning tier attributes based on the profile. On-demand data progression in a business hour will drive Compellent into crazy. If you are Citrix VDI mainstream than your workload is pretty much dead until data progression is complete.

A side effect of this technology is storage controller struggle to maintain on demand data progression and IO request at the same time hence there will be queue depth, and longer seek time in backend storage. In this situation, storage seek time is higher than normal.

Storage Profile: Storage profile in lay man’s terms is segregating expensive and cheap disk and profiling them in tier 1 (SSD RAID 10), tier 2 (15K Fibre Channel RAID 10, RAID 5, RAID 6) and tier 3 (7.2K SATA RAID 5, RAID 6). The storage profile determines how the system reads and writes data to disk for each volume as they are known in Compellent terms and how the data ages over time a feature called Data Progression. For example, random read request goes to tier 1 where you kept hot data, and a year old emails go to tier 3.

Storage Profiles supposed to allow the administrator to manage both writable blocks and replay blocks for a volume. It is fundamentally a tiering of storage in a controlled way. In theory, it supposed to be in a controlled environment. However, in reality, it does add extra workload to Dell Compellent controller. Let’s say you have tiered your storage according to your read and write intense IO. What happens when to READ and WRITE intense volume gets full?. Storage controller automatically triggers an on demand data progression from upper tier to lower tier to store data. Hence a WRITE intense IO is generated in lower tier what you wanted to avoid in the first place that’s why you profiled or tiered your storage. Mixing data progression with storage tiering defeats whole purpose of storage profiling.

Compellent Replay: Replay is essentially a storage snapshot in Dell terms. Dell Compellent Data Instant Replay software creates point-in-time copies called Replays. With Data Instant Replay Dell Compellent storage Replays at any time interval with minimal storage capacity. But here is the catch you will be most likely to run storage replay during the daily backup window. Backup generates lots of READ IOPS and Replays generate lots of READ and WRITE IOPS at the same time which is a daily backup window. Hence your backup is going to be dead slow. You will run out of the backup window and never be going to finish backup before the business hours. It will be a nightmare to fulfil data retention SLA and restore of any file systems and sensitive applications.

IOPS & Latency: Input/Output per second is a measurement unit of any hard disk and storage area network (SAN). This is a key performance matrix of a SAN regardless of manufacture, and this matrix remains unchanged. If you are to measure a SAN, this is where you begin. Never think that you have a bounce of virtual machines and it’s okay to buy SAN without IOPS consideration. There is the difference between a virtualised DHCP server and virtualised SQL server. A DHCP server may generate 20 IOPS but a SQL server can generate 5000 IOPS depends on what you are running on that SQL server. Every query you send to a SQL server or the application depends on the SQL server generate IOPS both read and write IOPS. For a Citrix XenApp and XenDesktop customer, you have to take into consideration that every time you launch a VDI session, open an word document, you generate IOPS, once you click save button on a word document, you generate write IOPS. Now you multiply the IOPS of each VDI session by the number of users, number of applications, number VDI and users inputs to estimate your real IOPS.

Now think about latency, in plain English, latency is the number of seconds or milli seconds you wait to retrieve information from a hard disk drive. This is calculated in round-trip between your request and the hard disk serve your request. Now you think millions of requests are bombarded on the storage area network. A SAN must sustain those requests and serve application requests, again it depends on what sort of workload you are running on a SAN. For example, file servers, Citrix profile, Citrix VDI, Exchange Server and SQL servers need low latency SAN.

In Dell Compellent, you may see volume IOPS e.g. 2000 but if you view disks hosting the same volume, then you might see 5000 IOPS. Then you must ask question how-come 5000-2000=3000 IOPS are generated automatically. Does Compellent has any tools to interrogate storage controller to see how additional workloads are generated? No it doesn’t. Your only bet is Dell support telling you the truth if you are lucky. The answer is automated RAID scrub is generating extra workloads on storage i.e. 3000 IOPS which could have been utilized for real workloads.

To co-relate this analysis with an all flash array storage, e.g. Dell Compellent, the SAN must be able to offer you the major benefits of a storage area network. If this storage cannot provide you low latency and high IO throughput for sensitive applications and workloads then you need to go back to drawing board or hire a consultant who can analyse your requirements and recommend you the options that match your need and budget. For further reading find Citrix validated solutions, storage best practices recommended by VMware and Microsoft. There are many tooling available in the market for you to analyse workload on applications, on a virtual or a physical infrastructure.

RAID Scrub: Data scrubbing is an error correction technique that uses a background task to inspect storage for errors periodically, and then correct detected errors using redundant data in the form of different checksums or copies of data. Data scrubbing reduces the likelihood that single correctable errors will accumulate, leading to reduced risks of uncorrectable errors.

In NetApp, you can schedule a RAID Scrub that suits your time and necessity however in Dell Compellent you cannot schedule a RAID Scrub through GUI or Command line. Dell technical support advised that this is an automated process takes places every day to correct RAID groups in Dell Compellent. There is a major side effect running automatic RAID scrub. RAID scrub will drive your storage to insane IOPS level, and latency will peak to high causing production volume to suffer and under perform. Performance of virtualisation will be degraded so badly that production environment will struggle to serve IO request. Dell advised that Dell can do nothing about RAID scrub because RAID scrub in SCOS operating systems is an automated process.

Compellent Multipathing: By implementing MPIO solution you eliminate any single point of failure in any physical path (s) and logical path(s) among any components such as adapters, cables, fabric switches, servers and storage. If one or more of these elements fails, causing the path to fail, multipathing logic uses an alternate path for I/O so that applications can still access their data. Each network interface card (in the iSCSI case) or HBA should be connected by using redundant switch infrastructures to provide continued access to storage in the event of a failure in a storage fabric component. This is the fundamental concept of any storage area network AKA SAN.

New generation SANs are integrated with multipath I/O (MPIO) support. Both Microsoft and VMware virtualisation architecture supports iSCSI, Fibre Channel and serial attached storage (SAS) SAN connectivity by establishing multiple sessions or connections to the storage array. Failover times may vary by storage vendor, and can be configured various way but the logic of MPIO remains unchanged.

New MPIO features in Windows Server include a Device Specific Module (DSM) designed to work with storage arrays that support the asymmetric logical unit access (ALUA) controller model (as defined in SPC-3), as well as storage arrays that follow the Active/Active controller model.

The Microsoft DSM provides the following load balancing policies. Microsoft load balance policies are generally dependent on the controller design (ALUA or true Active/Active) of the storage array attached to Windows-based computers.

Round-robin with a subset of paths
Dynamic Least Queue Depth
Weighted Path

VMware based systems also provide Fixed Path, Most Recently Used (MRU) and Round-Robin Configuration which is the most optimum configuration for VMware virtual infrastructure.

To explain ALUA in simple terms is that Server can see any LUN via both storage processors or Controller or NAS Head as active but only one of these storage processors “owns” the LUN. Both Storage Processor can view logical activities of storage using physical connection either via SAN switch to the server or via direct SAS cable connections. Hyper-v or vSphere ESXi server knows which processor owns which LUNs and sends traffic preferably directly to the owner. In case of controller or processor or NAS Head Failure Hyper-v or vSphere server automatically send traffic to an active processor without loss of any productivity. This is an essential feature of EMC, NetApp and HP products.

Let’s look at Dell Compellent now. Dell Compellent does not offer true Active/Active Controllers for any Storage. Dell Controllers Explained! Dell Verified Answer. Reference from Dell Forum….

“In the Compellent Architecture, both controllers are active. Failover is done at either the port or controller level depending on how the system was installed. Volumes are “owned” by a particular controller for mapping to servers. Changing the owning controller can be done – but it does take a volume down.”

I can confirm that this is exactly Dell Customer support advised me when I called them. Dell Compellent can take up to 60~90 seconds to failover from one controller to another. Which means entire virtual environment will go offline for a while and get back online. To update firmware or to replace a controller you have to bring everything down then bring everything back online which will cause a major outage and productivity loss for the entire organisation.

Multipathing options supported by the Host Utilities

Multipath I/O Overview

Multipathing Considerations

Dell Compellent is not an ALUA Storage Array

Performance Issue:  To identify Dell Compellent bottleneck for a virtualisation platform hosted in Compellent. Run the following in Windows perfmon in a virtual machine or a physical machine where a volume of Compellent storage is presented via HBA or iSCSI initiator. Use Windows perfmon, create a data collector set of the below attributes and generate a report using PAL tools. Extract seek time, latency, IOPS and queue depth in the Compellent storage. You will see a bottleneck in every area of storage you can expect. Read further on Windows Performance Monitoring Tools

\LogicalDisk\Avg. Disk Sec/Read

\LogicalDisk\Avg. Disk Sec/Write

\LogicalDisk\Disk Bytes/Sec

\LogicalDisk\Disk Reads/Sec

\LogicalDisk\Disk Writes/Sec

\LogicalDisk\Split IO/sec

\LogicalDisk\Disk Transfers/sec

Use the following Tools to analyse workloads and storage performance in your storage area network: 

Capacity planning & workload analysis tools

Multi-vendor storage performance and capacity monitoring


Windows Perfmon

PAL Analaysis Tools

Storage load generator / performance test tool

Dell EqualLogic Storage Management Pack Suite for SCOM

Monitoring EMC storage using SCOM 2012 SP1 with ESI Management Packs

IBM Storage Management Pack for Microsoft System Center Operations Manager

Cost Compare:

The cost of each gigabyte of storage is declining rapidly in every segment of the market. Enterprise storage today costs what desktop storage did less than a decade ago. So why are your overall costs increasing when buying storage? Let’s make it simple! Ask yourself questions?

How much will the storage cost? How much will the SAN cost to implement? How much will the SAN cost to operate? Now use the below tools to calculate the real cost of the owing black box?

Amazon EBS Pricing

Google Cloud Platform Pricing Calculator

Azure Storage Pricing

IBM TCO Calculator

vSAN Hybrid TCO and Sizing Calculator

HPE Business Value Calculator

Microsoft TCO Calculator

So what will you be looking in a SAN? 

  • Lower TCO
  • Storage Performance
  • Scale-to-Fit
  • Quality of Service
  • Uncompromised Availability and uptime
  • Cloud Ready
  • Reduction of Data (de-duplication)
  • Reduction of backup
  • Analytics and automation
  • Reduction of Data Centre footprint 

Summary: Dell Compellent makes a compelling argument for all-flash performance tiers. Yes, this argument is in sales pitch not in reality. A price conscious poor man who needs just any SAN and has a lower IO environment can have Compellent. For mainstream enterprise storage, Dell Compellent is a bad experience and can bring disaster to corporate Storage Area Network (SAN).

I had no doubt when Compellent introduced all flash arrays it was innovative but Compellent’s best days are gone. Just shop around, you will find better all-flash, converged, hybrid and virtual arrays which are built on better software, controllers and SSDs. There are flash arrays in the market which run clever codes and algorithm within the software to produce high IO, low latency and performance for sensitive applications.

Related Articles: 

EMC Unity Hybrid Storage for Azure Cloud Integration

Pro Tips For Storage Performance Testing

Storage Top 10 Best Practices

SQLIO download page

SQLIOSim tool KB article

SQL Server Storage Engine Team Blog

SQL Server I/O Basics

SQL Server I/O Basics – Chapter 2

Predeployment I/O Best Practices

Disk Partition Alignment Best Practices for SQL Server

EMC Symmetrix DMX-4 Enterprise Flash Drives with Microsoft SQL Server Databases

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