If you’re seeking a centralized storage device that provides traditional block-level storage for your physical or virtual servers, while simultaneously providing a central platform for file-level data storage, then you’re looking for a Unified Storage device. Traditionally, these devices do not contain atypical hardware that you wouldn’t already find in a block-level SAN, they are SANs with a NAS software feature. One way to loosely conceptualize the difference between a NAS and a SAN is that NAS appears to a client operating system as a file server (a client can map network drives to shares on that server) whereas a disk available through a SAN still appears to the client OS as a disk, which is visible in disk and volume management utilities (along with client's local disks), and is available to be formatted with a file system and mounted. The connectivity protocols for a SAN include Fibre Channel, iSCSI, whereas the popular NAS connectivity protocols used are NFS and CIFS. Unified Storage replaces file servers and consolidates data for applications and virtual servers onto a single platform.
NAS-specific storage devices are plentiful in the market, and many offer large, inexpensive, and redundant disk capacities and features usually found in a block-level SAN. Vendor examples include HP’s StoreEasy product family, which uses Microsoft Windows as a single-solution OS paired with a RAID array, and a crowded middle-market of NFS Linux-based disk devices that include Synology, Transporter, and QNAP. However, many of these products do not scale beyond their initial capacity, and can present too much of a failure risk for an Enterprise network. Unified storage can provide the cost savings and simplicity of consolidating storage over an existing network, the efficiency of tiered storage, and the flexibility required by virtual server environments.
Potential cost savings attract IT buyers to Unified Storage devices, because, while not every network requires a SAN, most networks have some flavor of a NAS concept implemented. End users need a shared and central location for storing heaps of documents and other data, and a common way of implementation is with Microsoft-based File Shares (accessed via the legacy SMB protocol or more commonly CIFS). As networks grow and age, these file share caches usually never shrink in size, which not only causes daily management consternation for the IT Admins, but also increases the vulnerability and importance of the network’s most-coveted data. File data has to be placed somewhere – why not give it the same efficiency and high availability features of a SAN?
Most of the popular Enterprise storage vendors have a Unified option. EMC’s current VNX-Series Generation can use dedicated RAM and CPU resources for Data Movers that can control CIFS traffic to dedicated LUNs. In 2002, NetApp added block-level capabilities to their popular Filer series, taking the reverse route to get to a Unified option. 3PAR StorServ, now owned by HP, offers the File Persona Software Suite to complement their Block Persona technology.
Management of Unified Storage is not complex. Hardware competition benefits buyers by having a single pane-of-glass interface for most NAS-functionality paired right along with day-to-day LUN provisioning for SANs. Security and Access integration with Microsoft Active Directory file permissions can get complex, but only for the most rigorous of Security initiatives.
Counter arguments to Unified Storage systems usually hover around perceived compromises in performance, because File-based I/O is structurally different that block-based I/O. If a block-based application is combined on a system that has more dynamic, file-based access, users can experience variability in performance because of resources allocated to the file-based side. Consistency in disk performance is paramount for many environments, and Unified Storage can be considered a potential risk.
Many IT Departments can see Unified Storage devices as unnecessary, as most already have Windows Server Virtual Machines providing Windows CIFS-based File Share vdisks on their existing block storage LUNs. The vdisks can scale easily, because NTFS-based volumes can potentially grow to 16TB. Most Windows-based networks also use Microsoft’s Group Policy to centrally manage File Share access, and adding another abstractive layer with a NAS device can create complexity where it is not desired.
With a Unified solution, administrators need to manage SAN and NAS storage as separate silos. This complicates administration, forcing them to predict future storage needs for each silo and manage requirements separately. Since File-Level storage is traditionally placed on less-expensive SATA disk, the Unified Solution will eventually be constrained to the limitations of the entire solution and rapidly accelerate a Storage refresh cycle.
Realistically, most Unified Storage Systems are better at one capability than the other. This means they are a NAS that figured out a way to provide block storage (NetApp), or they are block storage with some sort of NAS function integrated (EMC). Although most environments will use a mixture of workloads, a particular workload will often be the most important. Make sure that you test the specific conditions and configurations that will be most important to you.