Valuable Insight into Storage

Edit: It amazes me how much further we have come since I wrote this.

Originally posted April 10, 2012 on AIXchange

I recently took some online training that I found interesting and valuable. The webinar presenter, Norman Bogard, compares and contrasts network-attached storage (NAS) and storage area networks (SANs). (In his presentation Norman acknowledges Brett Cooper and Nils Haustein for their input, so I want to be sure to mention them here.)

When I think of early iterations of direct-attached storage, like SSA disks or regular internal SCSI disks, it amazes me how far we’ve come. Advances have been brought not just to storage hardware, but to the network infrastructure. Networks and switches are so much faster and more robust now.

The webinar opens with a review of the history of NAS and SAN and protocols like NFS, NCP, SMB and CIFS. Then some terminology is introduced. I’m paraphrasing and borrowing some of the language from the slide deck since Norman did such a good job of compiling the material:

“SAN, or block storage, will leverage Small Computer System Interface (SCSI) commands to read-write specific blocks. Common SCSI access methods include Fiber Channel (FC), Internet Small Computer System Interface (iSCSI), or InfiniBand (IB). InfiniBand is a high speed network interconnect.

“NAS, or file storage, reads and writes files instead of blocks. The NAS has control of the files, contrasted with a SAN where the server would have control over the files.  A file server is a storage server dedicated (primarily) to serving file-based workloads.

“A NAS gateway is a server that provides network-based storage virtualization. It provides protocol translation from host-based CIFS/NFS to Storage Area Network (SAN) based block storage. Examples of NAS gateways are IBM N series & SONAS; NetApp V Series; EMC VNX/Celerra; OnStor (LSI); HP P4000 Unified Gateway.

“Unified Storage is a single logical, centrally managed storage platform that serves both block (FC, iSCSI, IB) and file-based (CIFS, NFS, HTTP, etc.) workloads. Examples of Unified Storage includes IBM N series; NetApp V series; IBM Storwize V7000 Unified.

“When you compare NAS and SAN, you will find that they have similar concepts. For example, your redundancy for your SAN will come from your MPIO or SDD drivers, while redundancy for the NAS will come from teaming or trunking your network ports for resiliency or improved bandwidth, depending on how you have set things up.

“Your security for a SAN will come from LUN Masking and Zoning, while you would control access on the network the same way you always would, with things like VLANS, exports, and shares.

“Your physical connectivity to the SAN would come via the HBA, while your network traffic for the NAS would go out the same NIC that it always has, at least until converged network adapters become more widely deployed. Once we have converged adapters, all of the traffic will be network traffic, although you will then be dealing with more encapsulation of the different frames and protocols.

“Your underlying protocol on a SAN is SCSI, while you use the same IP/UDP protocols that you do with networking when you use NAS.

“You will call your SAN devices arrays, and you will present LUNs, while your NAS will have filers and data movers. You will have structured/relational data on a SAN, and unstructured data on a NAS.”

From there, Norman contrasts the concepts of block storage (SAN) and file storage (NAS). I’ll share more about this webinar in next week’s post.