The importance of networked storage

An SMB's data store is crucial for its operations. If things are not okay here, business losses will result. This is where networked storage options such as NAS, FC SAN and IP SAN can help

Enterprise storage has moved away from DAS (Direct Attached Storage) to the network. This is due to the performance, efficiency, and cost benefits that centralised, networked storage offers vis-à-vis distributed DAS. The issue is especially relevant for Indian SMBs which have much to gain from having a proper network storage infrastructure.

The options available in terms of networked storage are NAS (Network Attached Storage) and SAN (Storage Area Network). While both can be used by enterprises of any size, the small business (SB) has traditionally favoured NAS whereas the medium business (MB) has gone in for NAS and entry-level SAN (FC- and IP-based). However, newer options are promising to buck these trends.

On your LAN

As storage requirements of enterprises spiral up, DAS was not able to meet them. This is when NAS made its appearance on the LAN with the advantages of easy deployment, management and usability.

More importantly, NAS also brought about centralised storage for SMBs, unlike DAS’ distributed model. Earlier, this benefit was available only to large enterprises which used expensive SANs. This made NAS the most popular option for SMBs even though it uses slower file-based data access as opposed to the faster block-level access used in SANs.

A NAS is nothing but an array of off-the-shelf hard disks controlled by an operating system. These disks can also be connected in RAID configuration for better redundancy and availability. Newer serial ATA drives have ensured that NAS technology is getting cheaper with better performance.

The most popular NAS operating systems are NetApp’s Data Ontap, Microsoft’s Windows Storage Server 2003, and Adaptec’s GuardianOS. The Indian NAS market is dominated by Ontap (on devices from NetApp, IBM and HDS) and Storage Server 2003-based NAS devices from EMC, Dell and HP.

The operating system usually has built-in or additional tools for features such as backup and restore, mirroring, snapshot capability, etc. It is important to evaluate the functionality of these tools when choosing a NAS.

NAS gateways are a new option for organisations already having investments in FC (Fibre Channel) SAN. These devices come with FC, iSCSI, and Ethernet interfaces to connect to SANs and other environments. One of the main application areas for NAS gateways has been as nearline storage between SANs and tape-based backup.

Choosing a NAS solution

The primary lookout when shopping for NAS is the operating system and data tools. The operating system must be able to support Windows, Unix and Linux servers. Always opt for the NAS that offers the best toolset for your requirements, along with providing high availability features like mirroring and failover.

Next come NAS management and environment support. The NAS chosen should have a single point of management. It should also have support for common protocols like NFS, CIFS, NDMP and SNMP.

It is a good idea to go in for NAS devices that use SATA drives as these offer higher performance with lower costs.

At the high end

When it comes to top-level networked storage, SAN occupies prime position. These storage boxes use block-level data access for high-volume data access requirements.

SANs create a parallel network for data traffic between hard disk storage arrays (usually SCSI drives connected as RAID). This helps achieve higher data throughputs such as those required in banking and telecom. The options available in SANs are FC- and IP-based SANs.

Fibre to the SAN

FC SANs occupy the higher end of the SAN spectrum. In this type of SAN, the disk arrays are connected using fibre channel connections. FC is available at speeds of 1, 2, 4 and 10 Gbps.

An FC switch acts as the central point for control of data flowing through the SAN. The term ‘Director’ is used to represent SAN switches with over 64 FC ports. The disk arrays or JBOD (Just a Bunch of Ordinary Disks) are high-performance hard disk arrays connected in RAID configuration. Many commonly available disk arrays also have ‘intelligent’ features because of built-in software features.

SAN routers also deserve a mention here. These are devices that will be required if you plan to connect FC SANs to IP SANs and other environments.

Today, most vendors have entry-level FC SANs targeted at the SMB. These provide good value for enterprises looking at high-performance, low-cost entry into the SAN arena.

Tailored for the SMB

FC SANs still pose a high-cost entry barrier to SMBs, so their adoption level is currently low. In addition, most FC SANs still use highly proprietary technology leading to inter-operability and manageability issues. IP SANs are an attempt by various vendors to overcome these issues and tap into the SMB space.

An IP SAN uses the iSCSI protocol and Gigabit Ethernet over Cat 6 cabling to network disk arrays using a TCP/IP network. These SANs provide native-level block access and data transfer, and are similar in this respect to traditional FC SANs.

IP SANs are available in two physical configurations:

• Physically separate controller, switch and disk array units
• Single integrated controller, switch and disk array unit.

IP SANs have fewer inter-operability and management issues, being based on existing TCP/IP technology. This also makes it easier to train administrators on IP SANs than on FC SANs.

Although IP SANs offer lower performance, they are ideal for SMBs that do not require the higher data throughputs of FC SANs. With the availability of 10 Gigabit Ethernet (GbE) technology, IP SANs have the potential for higher speeds. However, IP SANs based on 10 GbE are yet to reach the market.

SAN selection

When choosing a SAN (FC or IP), some features to look out for are the number of servers that can connect to an array, RAID levels supported, and minimum/maximum capacities.

Some of the array features to look out for in FC SANs are logical unit numbers, and connection types supported (FC, FICON, ESCON, SCSI, etc). Host connectivity options also have to be checked.

Features to look out for in FC and IP SANs include the number of controllers, automatic I/O path failover, and redundancy in components. The switch should also have management software with availability and SAN security features. VSAN (Virtual SAN) capability is yet another useful feature to have which will help virtually separate distinct SAN within a SAN.

It is important to check the compatibility of management software with infrastructure/storage management tools and operating systems used by the enterprise. Inter-operability with products from other vendors is also desirable.

Product support offered by the SAN vendor comes next. All the details such as onsite support, warranty, extension of warranty, time to resolution, parts and labour costs have to be verified before selecting the solution. In addition, it is a good idea to find out ongoing costs associated with the SAN at the time of selection itself. If possible, try out a pilot project to check the vendor’s claims.