I hear the terms that NAS is file-oriented storage while SAN is block oriented. Yet NAS can share files by various...
locking schemes so I'm not sure as to the advantage or disadvantage of block versus file storage architectures. Besides the effects of NAS requests going up and down the IP stack, are there really any performance penalties in a Gigabit Ethernet versus a Fibre Channel SAN? Do you have a good white paper or reference that can explain, at a low level, the difference between the two architectures?
Network Attached Storage provides data as a remote file system. Basically, a redirector on the server where the application is executing turns a file request for data into a remote file system access via TCP/IP over the local area network. The NAS device handles the network request and turns that into direct block I/O for the data. So, even though accessing data over the network is a file operation, the NAS device turns it into a block I/O operation.
File accesses over the network were the original protocols developed for networks by implementations of NFS and CIFS the most commonly used remote file system access software. Block I/O is what a device understands, so at some point the I/O must be turned into a block access such as a SCSI command (over a SCSI bus, Fibre Channel, etc.). The performance issues are: the introduced latency due to this conversion; traversing the TCP/IP protocol stack; the physical connection; and competition for the resource. (Bad things happen when the network gets congested). The actual bit rate of the interface is a very misleading number. For example, Gigabit Ethernet should transfer data at 100 MB/s but the average transfer rate is much less than that because of various overhead along the way. Fibre Channel is typically 95% efficient due to the fact that it is a hardware intensive implementation (at a cost obviously) with special information passed to do things such as pre-allocating hardware buffers, etc.
We teach a seminar where we go into details about the whys and wherefores of the differences but have not specifically written a paper on it. I have not seen an objective paper on the differences. Unfortunately, vendor papers are trying to sell their product and that should always be taken into consideration.
Related Q&A from Randy Kerns
What is the one hidden gotcha that you'd advise users about if they were shopping for an all-flash storage array?continue reading
How much control do you have with all-flash storage arrays? How much control do you have over how arrays handle your data? Do you control the caching?continue reading
Vendors often publish numbers for 'usable' capacity versus 'effective' capacity. Can you explain this and how can you plan flash capacity needs with ...continue reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.