NAS Devices
A NAS device is
optimized for file-serving functions such as storing, retrieving, and
accessing files for applications and clients. As shown below
a general-purpose server can be used to host any application because it
runs a general-purpose operating system. Unlike a general-purpose
server, a NAS device is dedicated to file-serving. It has specialized
operating system dedicated to file serving by using industry-standard
protocols. Some NAS vendors support features, such as native clustering
for high availability.
General purpose server versus NAS device
NAS offers the following benefits:
A NAS device has two key components: NAS head and storage. In some NAS implementations, the storage could be external to the NAS device and shared with other hosts. The NAS head includes the following components:
Unified NAS performs file serving and storing of file data, along with providing access to block-level data. It supports both CIFS and NFS protocols for file access and iSCSI and FC protocols for block level access. Due to consolidation of NAS-based and SAN-based access on a single storage platform, unified NAS reduces an organization's infrastructure and management costs.
- Comprehensive access to information: Enables efficient file sharing and supports many-to-one and one-to-many configurations. The many-to-one configuration enables a NAS device to serve many clients simultaneously. The one-to-many configuration enables one client to connect with many NAS devices simultaneously.
- Improved efficiency: NAS delivers better performance compared to a general-purpose file server because NAS uses an operating system specialized for file serving.
- Improved flexibility: Compatible with clients on both UNIX and Windows platforms using industry-standard protocols. NAS is flexible and can serve requests from different types of clients from the same source.
- Centralized storage: Centralizes data storage to minimize data duplication on client workstations, and ensure greater data protection
- Simplified management: Provides a centralized console that makes it possible to manage file systems efficiently
- Scalability: Scales well with different utilization profiles and types of business applications because of the high-performance and low-latency design
- High availability: Offers efficient replication and recovery options, enabling high data availability. NAS uses redundant components that provide maximum connectivity options. A NAS device supports clustering technology for failover.
- Security: Ensures security, user authentication, and file locking with industry-standard security schemas
- Low cost: NAS uses commonly available and inexpensive Ethernet components.
- Ease of deployment: Configuration at the client is minimal, because the clients have required NAS connection software built in.
A NAS device has two key components: NAS head and storage. In some NAS implementations, the storage could be external to the NAS device and shared with other hosts. The NAS head includes the following components:
- CPU and memory
- One or more network interface cards (NICs), which provide connectivity to the client network. Examples of network protocols supported by NIC include Gigabit Ethernet, Fast Ethernet, ATM, and Fiber Distributed Data Interface (FDDI).
- An optimized operating system for managing the NAS functionality. It translates file-level requests into block-storage requests and further converts the data supplied at the block level to file data.
- NFS, CIFS, and other protocols for file sharing
- Industry-standard storage protocols and ports to connect and manage physical disk resources
The NAS environment includes clients accessing a NAS device over an IP network using file-sharing protocols.
Components of NAS
Unified NAS performs file serving and storing of file data, along with providing access to block-level data. It supports both CIFS and NFS protocols for file access and iSCSI and FC protocols for block level access. Due to consolidation of NAS-based and SAN-based access on a single storage platform, unified NAS reduces an organization's infrastructure and management costs.
A unified NAS contains
one or more NAS heads and storage in a single system. NAS heads are
connected to the storage controllers (SCs), which provide access to the
storage. These storage controllers also provide connectivity to iSCSI
and FC hosts. The storage may consist of different drive types, such as
SAS, ATA, FC, and flash drives, to meet different workload requirements.
Unified NAS connectivity
Three common NAS implementations are unified, gateway, and scale-out. The
unified NAS consolidates NAS-based and SAN-based data access within a unified
storage platform and provides a unified management interface for managing both
the environments.
In a gateway implementation, the NAS device uses external storage to store
and retrieve data, and unlike unified storage, there are separate
administrative tasks for the NAS device and storage.
The scale-out NAS implementation pools multiple nodes together in a
cluster. A node may consist of either the NAS head or storage or both. The
cluster performs the NAS operation as a single entity.
InfiniBand is a networking technology that provides a low-latency, high-bandwidth communication link between hosts and peripherals. It provides serial connection and is often used for inter-server communications in high-performance computing environments. InfiniBand enables remote direct memory access (RDMA) that enables a device (host or peripheral) to access data directly from the memory of a remote device. InfiniBand also enables a single physical link to carry multiple channels of data simultaneously using a multiplexing technique. The InfiniBand networking infrastructure consists of host channel adapters (HCAs), target channel adapters (TCAs), and InfiniBand switches. HCAs are located within hosts. HCAs provide the mechanism to connect CPUs and memory of the hosts to the InfiniBand network. Similarly, TCAs enable storage and other peripheral devices to connect to the InfiniBand network. InfiniBand switches provide connectivity among HCAs and TCAs.
7.6 NAS Implementations
Three common NAS implementations are unified, gateway, and scale-out. The unified NAS consolidates NAS-based and SAN-based data access within a unified storage platform and provides a unified management interface for managing both the environments.
In a gateway implementation, the NAS device uses external storage to store and retrieve data, and unlike unified storage, there are separate administrative tasks for the NAS device and storage.
The scale-out NAS implementation pools multiple nodes together in a cluster. A node may consist of either the NAS head or storage or both. The cluster performs the NAS operation as a single entity.
7.6.1 Unified NAS
Unified NAS performs file serving and storing of file data, along with providing access to block-level data. It supports both CIFS and NFS protocols for file access and iSCSI and FC protocols for block level access. Due to consolidation of NAS-based and SAN-based access on a single storage platform, unified NAS reduces an organization's infrastructure and management costs.
A unified NAS contains one or more NAS heads and storage in a single system. NAS heads are connected to the storage controllers (SCs), which provide access to the storage. These storage controllers also provide connectivity to iSCSI and FC hosts. The storage may consist of different drive types, such as SAS, ATA, FC, and flash drives, to meet different workload requirements.
7.6.2 Unified NAS Connectivity
Each NAS head in a unified NAS has front-end Ethernet ports, which connect to the IP network. The front-end ports provide connectivity to the clients and service the file I/O requests. Each NAS head has back-end ports, to provide connectivity to the storage controllers.
iSCSI and FC ports on a storage controller enable hosts to access the storage directly or through a storage network at the block level. Figure 7.5 illustrates an example of unified NAS connectivity.
7.6.3 Gateway NAS
A gateway NAS device consists of one or more NAS heads and uses external and independently managed storage. Similar to unified NAS, the storage is shared with other applications that use block-level I/O. Management functions in this type of solution are more complex than those in a unified NAS environment because there are separate administrative tasks for the NAS head and the storage. A gateway solution can use the FC infrastructure, such as switches and directors for accessing SAN-attached storage arrays or direct-attached storage arrays.
The gateway NAS is more scalable compared to unified NAS because NAS heads and storage arrays can be independently scaled up when required. For example, NAS heads can be added to scale up the NAS device performance. When the storage limit is reached, it can scale up, adding capacity on the SAN, independent of NAS heads. Similar to a unified NAS, a gateway NAS also enables high utilization of storage capacity by sharing it with the SAN environment.
Figure 7.5 Unified NAS connectivity
7.6.4 Gateway NAS Connectivity
In a gateway solution, the front-end connectivity is similar to that in a unified storage solution. Communication between the NAS gateway and the storage system in a gateway solution is achieved through a traditional FC SAN. To deploy a gateway NAS solution, factors, such as multiple paths for data, redundant fabrics, and load distribution, must be considered. Figure 7.6 illustrates an example of gateway NAS connectivity.
Figure 7.6 Gateway NAS connectivity
Implementation of both unified and gateway solutions requires analysis of the SAN environment. This analysis is required to determine the feasibility of combining the NAS workload with the SAN workload. Analyze the SAN to determine whether the workload is primarily read or write, and if it is random or sequential. Also determine the predominant I/O size in use. Typically, NAS workloads are random with small I/O sizes. Introducing sequential workload with random workloads can be disruptive to the sequential workload. Therefore, it is recommended to separate the NAS and SAN disks. Also, determine whether the NAS workload performs adequately with the configured cache in the storage system.
7.6.5 Scale-Out NAS
Both unified and gateway NAS implementations provide the capability to scale-up their resources based on data growth and rise in performance requirements. Scaling up these NAS devices involves adding CPUs, memory, and storage to the NAS device. Scalability is limited by the capacity of the NAS device to house and use additional NAS heads and storage.
Scale-out NAS enables grouping multiple nodes together to construct a clustered NAS system. A scale-out NAS provides the capability to scale its resources by simply adding nodes to a clustered NAS architecture. The cluster works as a single NAS device and is managed centrally. Nodes can be added to the cluster, when more performance or more capacity is needed, without causing any downtime. Scale-out NAS provides the flexibility to use many nodes of moderate performance and availability characteristics to produce a total system that has better aggregate performance and availability. It also provides ease of use, low cost, and theoretically unlimited scalability.
Scale-out NAS creates a single file system that runs on all nodes in the cluster. All information is shared among nodes, so the entire file system is accessible by clients connecting to any node in the cluster. Scale-out NAS stripes data across all nodes in a cluster along with mirror or parity protection. As data is sent from clients to the cluster, the data is divided and allocated to different nodes in parallel. When a client sends a request to read a file, the scale-out NAS retrieves the appropriate blocks from multiple nodes, recombines the blocks into a file, and presents the file to the client. As nodes are added, the file system grows dynamically and data is evenly distributed to every node. Each node added to the cluster increases the aggregate storage, memory, CPU, and network capacity. Hence, cluster performance also increases.
Scale-out NAS is suitable to solve the “Big Data” challenges that enterprises and customers face today. It provides the capability to manage and store large, high-growth data in a single place with the flexibility to meet a broad range of performance requirements.
7.6.6 Scale-Out NAS Connectivity
Scale-out NAS clusters use separate internal and external networks for back-end and front-end connectivity, respectively. An internal network provides connections for intracluster communication, and an external network connection enables clients to access and share file data. Each node in the cluster connects to the internal network. The internal network offers high throughput and low latency and uses high-speed networking technology, such as InfiniBand or Gigabit Ethernet. To enable clients to access a node, the node must be connected to the external Ethernet network. Redundant internal or external networks may be used for high availability. Figure 7.7 illustrates an example of scale-out NAS connectivity.
Figure 7.7 Scale-out NAS with dual internal and single external networks
InfiniBand
InfiniBand is a networking technology that provides a low-latency, high-bandwidth communication link between hosts and peripherals. It provides serial connection and is often used for inter-server communications in high-performance computing environments. InfiniBand enables remote direct memory access (RDMA) that enables a device (host or peripheral) to access data directly from the memory of a remote device. InfiniBand also enables a single physical link to carry multiple channels of data simultaneously using a multiplexing technique. The InfiniBand networking infrastructure consists of host channel adapters (HCAs), target channel adapters (TCAs), and InfiniBand switches. HCAs are located within hosts. HCAs provide the mechanism to connect CPUs and memory of the hosts to the InfiniBand network. Similarly, TCAs enable storage and other peripheral devices to connect to the InfiniBand network. InfiniBand switches provide connectivity among HCAs and TCAs. 