Table of Contents
Enterprise Storage Systems
There is a substantial difference between NAS and SAN, the two storage systems that are increasing their popularity at the expense of traditional storage. Analysts have estimated that the use of both NAS and SAN technologies continues to grow.
At first glance there would be no difference between NAS and SAN, on the contrary, they might seem almost identical considering that many times they work under the same conditions. After all, both generally use RAID controllers connected to a network, which are backed up on a tape.
However, below are some differences that can seriously affect the way your data is used.
Cables & Protocols
Many people focus on cables, but the difference in protocols is currently the most important factor. For example, a common argument is that SCSI is faster than the ethernet so it’s better. Why?
Mainly, IT Mangers say that TCP / IP overhead cuts the efficiency of data transfer. So a Gigabit Ethernet gives you a 60-80 Mbps transfer against 100 Mbps.
But let’s consider this: the next version of iSCSI will double the speed; the next version of the ethernet protocol (available in beta today) will multiply the speed by a factor of 10. Which will be faster then? Even with the overhead? It is something to consider.
CABLES
NAS uses TCP / IP networks: Ethernet, FDDI, ATM (or TCP / IP on Fiber Channel).
SAN uses Fiber Channel.
PROTOCOLS
NAS uses TCP / IP and NFS / CIFS / HTTP.
SAN uses Encapsulated SCSI.
Other differences between NAS and SAN
NAS
At least every machine that can connect to the LAN (or is interconnected to the LAN through a WAN) can use NFS, CIFS, SMB or HTTP protocols to connect to a NAS and share files.
SAN
Only machines classified as servers equipped with Fiber Channel SCSI can connect to the SAN. The SAN Fiber Channel has a limit of approximately 10 km at most.
A NAS identifies data by file name and byte offsets, transfers data files or meta-data files (file owner, permissions, creation date, etc.), administers security, user authentication, file locking.
A SAN directs data through the number of disk blocks and transfers raw disk blocks.
A NAS allows better sharing of information especially between disparate operating systems such as Unix and NT.
File sharing is dependent on the operating system and is even non-existent in many operating systems.
The File System is administered by the main NAS unit.
The File System is administered by the individual servers.
Backups and mirrors (using features like NetApp Snapshots) are performed on files, not blocks, to save bandwidth and time. A Snapshot may be smaller compared to the volume of its source.
Backups and mirrors require a block-by-block copy, even if the blocks are empty. A mirror machine must be equal to or greater in capacity compared to the source volume.
NAS and SAN will continue to go head-to-head for the next few years, but over time, the differences between NAS and SAN will tend to merge, with the development new iterations of SCSI over IP and Open Storage Networking (OSN).
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