A storage server is a type of server used to store and manage digital data and acts as a backup server to store backup data. A storage server will be used for storing both small and large amount of data over a shared network. Although the need for storage is evident, it is not always clear which solution is right for your organization. There are a variety of options available, the most prevalent are direct-attached storage (DAS), network-attached storage (NAS) and storage area networks (SAN). Choosing the right storage solution can be as personal and individual decision. There is no one right answer for everyone. Instead, it is important to focus on the specific needs and long-term business goals of your organization. Several key criteria to consider include:
1 – Capacity
2 – Performance
3 – Scalability
4 – Availability & reliability
5 – Data protection
6 – IT staff and Resources available
7 – Budgets concern
DAS (Direct Attached Storage):
Direct Attached Storage (DAS) is a digital storage device that is attached directly to a server or PC via cable, meaning that DAS is not a part of the storage network. A DAS device may be an internal or external hard disk drive like internal hard drive in PC. These disk drives can be protected with different RAID levels, depending on data importance and criticality. For the server, a DAS storage is very much similar to its own internal drive or an external drive that has been plugged in.
The main interfaces used for DAS connection include Advanced Technology Attachment (ATA), Serial Advanced Technology Attachment (SATA), eSATA, Small Computer System Interface (SCSI), Serial Attached SCSI (SAS), and Fiber Channel.
It is worth mentioning that high access rate due to network absence, capability of storage capacity extension, data security and fault tolerance are some of advantages of DAS. However, the primary benefits of DAS include low cost and simplicity. Since it does not need components of network storage systems such as routers, switches and appropriate cabling and connections. The drawback of DAS is that it is not accessible by multiple user groups and only one user at a time is allowed.
DAS is the most basic level of storage. The storage devices are part of the host computer or directly connected to a single server, in which the workstation must access the server in order to connect to the storage device. On the opposite side, NAS and SAN are connected to workstation and servers over a network. In the DAS, if the server is down or experiencing problems, users can not store and access data. Surveillance images cannot be retrieved or stored. If the organization grows and needs new servers, storage for each server must be administered separately.
NAS (Network Attached Storage):
NAS is a type of file storage device that connects to a network. NAS devices, which typically do not have a keyboard or display, provide Local Area Network (LAN) nodes with file storage through a standard Ethernet connection. In fact, NAS employs an Ethernet connection for sharing files over the network.
Each NAS on the LAN acts as an independent network node which has its own IP address. Since the NAS device has an IP address, it will be accessible over the network via that IP address. NAS devices can be built with single drive or multiple drives. The latter provides higher capacity and greater data protection.
The existence of multiple computers on the network, is a candidate for using a network attached storage (NAS) device. Some NAS servers are just used for backing up and sharing files across the network, while others can do more tasks, such as sharing a printer among the networked PCs, acting as a media streamer or even a surveillance system by supporting IP cameras.
NAS has benefits such as good reading and writing performance, good data redundancy and protection options, offering security via data encryption, sharing files, backing up data from Windows, Mac, and possibly Linux machines and offering some cloud service for storage and backup.
The application of NAS in homes is storing and serving multimedia files and automated backup. For instance, many smart TVs use NAS to provide centralized storage. If a NAS device has a server mode, it can also act as an email, multimedia, database or print server for a small business. In enterprise level, a NAS array can be used as a backup for archiving and recovery. Also, some NAS products can hold enough disks to support RAID for greater data protection.
For those systems that must store a large amount of videos/images for many days, NAS is a good option. Network-Attached Storage comprised of both hard disks and management software. NAS serves files over a network. As a result, NAS relieves the server of storage and file serving responsibilities and provides more flexibility in data access, because of its independence.
SAN (Storage Area Network):
A Storage Area Network (SAN) is a secure high-speed data transfer network in which storage devices can access to multiple servers. It is a high-performance storage network that transfers data between servers and storage devices separate from local area network. SAN is often used where larger areas of high-speed storage and fast input-output space is required.
In contrast to DAS or NAS, which are optimized for data sharing at the first level, the strength of the SAN lies in its ability to move large blocks of data. This is so important for Band-Width intensive applications such as IP/Megapixel camera system recording. It provides block-level storage, meaning that when a host wants to access a storage device, it sends a block-based access request for that storage device. SAN storage devices include disk-based devices like RAID.
SAN implementation which is in two following types, leads to consistent and secure data transferring. Depending on what type is used, different types of cabling, protocols and routing equipment are used.
- Fiber channel (FC): Storage and servers are connected through a high-speed network of unified fiber channel switches. This is used for mission-critical applications where continuous data access is required. Fiber channel provides data retrieval speed more than 5 Gbps.
- Internet Small Computer System Interface (ISCSI) Protocol: SCSI is a standard used to communicate between servers and storage devices. By this infrastructure, the flexibility of a low-cost IP network is achieved.
In a SAN network, data transferring from one storage to another is conducted without or with minimal server intervention. SAN provides dynamic failover protection which means if a server fails or goes offline for maintenance, network operation continues. Also, additional capacity can be added to SAN as required. These, are the advantages of SAN. The main disadvantages of SANs are cost and complexity. Because SAN hardware is expensive and also building and managing a SAN, require a special skill set.
The distributed architecture of SAN enables it to offer higher level of performance and reliability. SANs provide fast data transfer while reducing latency and server workload.
VSA (Virtual Storage Appliance):
Virtual Storage Appliance (VSA) is a storage controller which runs on a virtual machine to create a shared storage without the need of additional hardware. It presents either file-level or block-level storage to the network.
VSA is not a connected physical device to any specific hardware. It uses the host system’s local disk for storage as a virtual disk or it can access to local physical drives directly. In fact, the VSA creates a virtual storage area similar to networked storage by incorporating direct-attached capacity on each physical host. Small businesses that need redundancy and high availability for shared storage and also large enterprises which transfer data between various arrays, are good usage candidates for the virtual storage appliance.
The differences between NAS, SAN and DAS:
NAS differs from a SAN in the way they distribute storage to other devices, meaning that the main difference between these two, is access protocols. NAS supports data storage under CIFS and NFS protocols (file-level), while access protocols in SAN are ISCSI and Fiber channel (block level).
On the other hand, it may seem, DAS is faster than any other storage methods. Since it needs data transferring over the network, while all data transferring will be occurred on a dedicated connection between the server and the storage device. However, due to high speed connection of fiber channel, in some cases SAN presents faster speed compared to speed provided by DAS. Also, Since SAN separates storage from the servers and incorporates them in a place where it can be accessed by any application, it provides better flexibility, availability and storage performance compared to DAS for large organization. So, due to the improved storage performance of SAN, organizations won’t need additional storage hardware, which saves money, although SAN hardware can be costly. Moreover, separating storage device from the servers, allows computing resources on the servers to perform other tasks not related to storage.
On the other hand, the difference between DAS and Network Attached Storage (NAS) is that a DAS device connects directly to a server without a network connection. DAS gives good performance, but there are limitations like the number of servers that can access to it. Also DAS storage has to be near to the server in the same rack. The advantage of NAS over DAS is that it simplifies file sharing among multiple users. The main difference is about how the computer or the server treats a particular storage. If the server’s processor is responsible for managing the attached storage, it will be some type of DAS and if the computer or the server treats the attached storage as another computer, which shares its data through the network, then it is a NAS.
Using storage servers for NVR and DVR:
Video surveillance requirements for high storage capacity and increasing the retention period, make the NVR or DVR to utilize the external storage servers in order to achieve a desired surveillance system. Regardless of format, both DVRs and NVRs can employ external storages presented in previous sections for improved capacity and reliability.
DAS has been the most implemented storage device in DVRs, so that it has generally became the part of this recording system. For medium and large scale video surveillance where performance, reliability and scalability of the storage system are important issues, newer external storages like SAN and NAS are more helpful than fixed DAS storage.
The storage component may be internal, fixed DAS storage, or may employ some type of external storage. Also, the other major component of surveillance system is the DVR or NVR which as engine of the entire system manages one or more cameras and the storage subsystem. Video frames from cameras are transferred from the DVR or NVR to the storage system. So choosing the appropriate storage device to achieve capacity and reliability, leads to a great surveillance system.