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CIT 361: Week 15

NAS, SAN, the Cloud, & more

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To start this lesson let us look at some of the history behind mass storage systems. At first the major developments were dedicated to building larger individual hard drives, which over time went from 5MB (megabytes) to 32MB, 320-500MB, then various GB (gigabytes) sizes, and now a fast USB 3, portable 2TB (terabytes) unit can be purchased for about $100. These individual drives are fine for personal storage and worked well as storage on network servers to which a few people could save large amounts of data or many could each store a few critical files based on storage quotas. But with current trends people have needed much more storage capacity and corporate law changes (such as the Sarbanes–Oxley Act in the wake of the Enron/Arthur Andersen documents destruction) have forced retaining comprehensive backups for longer time periods. So other solutions are now necessary.

RAID, originally redundant array of inexpensive disks but now often known as redundant array of independent disks, has been around for quite a long time at multiple levels. RAID 0 or striping, RAID 1 or mirroring, and RAIDs 5 & 6 as variants of block level striping with parity are among the more common forms. Striping (RAID 0) breaks large files into blocks that are saved simultaneously across two or more drives to provide both faster and larger file storage at the increased risk for data loss should a drive fail. Mirroring (RAID 1) improves security by simultaneously saving complete copies of each file to two drives at the loss of total storage capacity. RAID 5 and 6 attempt to improve security, capacity, and speed by using three or more drives to save striped data blocks along with computed parity blocks so that the loss or 1 drive (or with RAID 6 even 2 or more drives) does not result in a system failure or data loss. RAID arrays of 8 to 60 or more terabyte capacity are now fairly common.

Many RAID systems have been based on SCSI (pronounced scuzzy, small computer system interface) which greatly improved read and write speeds. More recently, the SCSI protocols have been adapted to network systems which thus allow storage to be spread across networks and even over the Internet. By mixing RAID's mirroring and data striping techniques over networks, iSCSI makes it possible to have high speed, simultaneous, multiple data copies saved at more than one location thus greatly improving data security in the event of catastrophic local events such as fires, earthquakes, hurricanes, etc.


NAS (network attached storage) and SAN (storage area network) are more recent developments in shared, high capacity data storage. While not mutually exclusive, these are not the same. To quote Wikipedia, "One way to loosely conceptualize the difference between a NAS and a SAN is that NAS appears to the client OS (operating system) as a file server (the 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, visible in disk and volume management utilities (along with client's local disks), and available to be formatted with a file system and mounted."

In writing this lesson, I just realized that the first computer network I installed in the early 1980s could have been described as a SAN, although the term did not exist at that time. It was a Corvus Omninet connected hard drive for Apple II computers. Since Apple DOS was limited to 140 kilobyte floppy disks the Corvus hard drive was partitioned into about 35 floppy sized volumes so that an Apple computer with this drive acted as if it had multiple floppy drives attached to it. The system I installed had 3 Apple II computers sharing a single 5MB Corvus drive on a network. Each Apple was alloted a specific set of partitions; 30 of which were dedicated to one Apple's functions. We have come a very long way since then.

Cloud storage, Cloud computing, etc.

Amazon Cloud Drive, Apple's iCloud, Dropbox, Google Cloud Storage, Microsoft's OneDrive, and others have developed cloud storage systems that individual users can subscribe to; sometimes a small amount of storage is provided at no cost and larger quantities can be leased at various rates. There are also a number of companies that provide cloud storage for businesses in whatever capacities are needed. Some of these systems, like Dropbox, allow you to give password protected shared read only or read/write access to your cloud space.

In addition to simple storage, many companies now offer flexible cloud computing solutions so that a businesses do not need to buy additional server capacity. These include Amazon Web Services, Google Cloud Platform, Microsoft Cloud Platform, and SAS Cloud, among others. Some of these systems provide only specific services such as web hosting while others provide office, database, analytical software and more customized to each business's needs. With these more full service cloud systems one gets computing power and networking capabilities as well as data storage.

Convenience to let others hire and train professionals that maintain computing systems and flexibility to increase or decrease computing resources as needed are major advantages for cloud based systems. However, these should be weighed against potential network outages, cloud host bankruptcies, security, and other potential concerns. For example, with bankruptcy US law essentially allows the court full jurisdiction to cancel all contractual obligations and decide what is a salable asset so that creditors can be repaid. So if your company's valuable data is stored on a bankrupt company's servers then any contract you had becomes void and that data can be sold to the highest bidder. Or, what happens if the cloud system is hacked and your data is stolen by cyberthieves?

Once again I think there is plenty of material for you to write about in this week's discussion.