Difference between a Storage Area Network and Network Attached Storage

If you are managing your own infrastructure in your own private data center, then you are bound to go through a selection of different storage offerings. Selecting a storage solution pretty much depends on your requirement. Before finalizing a particular storage option for your use case, a little bit of understanding about the technology is always helpful.

I was actually going to write an article about object storage (which is the current hottest storage option in the cloud). But before going and discussing that part of the storage arena, I thought its better to discuss the two main storage methods which co-exists together from a very long time, used by companies internally for their needs.

The decision of your storage type will depend on many factors like the below ones.

Type of data that you want to store
Usage pattern
Scaling concerns
Finally your budget

When you begin your career as a system administrator, you will often hear your colleagues talking about different storage methods like SAN, NAS, DAS etc. And without a little bit of digging, you are bound to get confused with different terms in storage. The confusion arises often because of the similarities between the different approaches in storage. The only hard and fast rule to stay up to date in technical terms, is to keep on reading stuffs (especially concepts behind a certain technology.)

Today we will be discussing two different methods that defines the structure of storage in your environment. Your choice of the two in your architecture should only depend on your use case, and type of data that you store.

By the end of this tutorial, I hope you will have a clear picture about the main two types of storage methods, and what to select for your need.

SAN (Storage Area Network) and NAS(Network Attached Storage)

The main things that differentiate each of these technologies are mentioned below.

The main things that differentiate each of these technologies are mentioned below.

How a storage is connected to a system. In short how the connection is made between the accessing system and the storage component (directly attached or network attached)
Type of cabling used to connect. In short this is the type of cabling done to connect a system to the storage component (eg. Ethernet & Fiber channel)
How are input and output requests done. In short this is the protocol used to conduct input and output requests (eg. SCSI, NFS, CIFS etc)

Related: How to monitor IO on linux

Let's discuss SAN first and then NAS, and at the end, let's compare each of these technologies to clear the differences between them.

SAN(Storage Area Network)

Today's applications are very much resource intensive, due to the kind of requests that needs to be processed simultaneously per second. Take example of an e-commerce website, where thousands of people are making orders per second, and all needs to be stored properly in the database for later retrieval. The storage technology used to store such high traffic data bases must be fast in request serving and response(in short it should be fast in Input and Output).

Related: Web server Performance test

In such cases(where you need high performance, and fast I/O ) we can use SAN.

SAN is nothing but a high speed network that makes connections between storage devices and servers.

Traditionally application servers used to have their own storage devices attached to them. Server's talk to these devices by a protocol known as SCSI(Small Computer System Interface). SCSI is nothing but a standard used to communicate between servers and storage devices. All normal hard disks, tape drives etc uses SCSI. In the beginning the storage needs of a server was fulfilled by a storage devices that was included inside the server(the server used to talk to those internal storage device, using SCSI. This is very much similar to how a normal desktop talks to its internal hard disk.).

Devices like Compact Disk drives are attached to the server(which are part of the server) using SCSI. The main advantage of SCSI for connecting devices to a server was its high throughput. Although this architecture is sufficient for low end requirements, there are few limitations like the below mentioned ones.

The server can only access data on the devices, which are directly attached to it.
If something happens to the server, access to data will fail (because the storage device is part of the server and is attached to it using SCSI)
There is a limit in the number of storage devices the server can access. In case the server needs more storage space, there will be no more space that can be attached, as the SCSI bus can accommodate only a finite number of devices.
Also the server using the SCSI storage has to be near the storage device(because parallel SCSI, which is the normal implementation in most computer's and servers, has some distance limitations. It can work up to 25 meters.)

Some of these limitations can be overcame using DAS (Directly Attached Storage). The media used to directly connect storage to the server can be any one of SCSI, Ethernet, Fiber channel etc.). Low complexity, Low investment, Simplicity in deployment caused DAS to be adopted by many for normal requirement's. The solution was good even performance wise, if used with faster mediums like fiber channel.

Even an external USB drive attached to a server is also a DAS(well conceptually its DAS, as its directly attached to the server's USB bus). But USB drives are normally not used due to the speed limitation of USB bus. Normally for heavy and large DAS storage solutions, the media used are SAS(Serially attached SCSI). Internally the storage device can use RAID(which normally is the case) or anything to provide storage volumes to servers. SAS storage options provide 6Gb/s speed these days.

An example of DAS storage device is Dell's MD1220

To the server, a DAS storage will appear very much similar to its own internal drive or an external drive that you plugged in.

Although DAS is good for normal needs and gives good performance, there are limitations like the number of servers that can access it. Storage device, or say DAS storage has to be near to the server (in the same rack or within the limits of the accepted distance of the medium used.).

It can be argued that, directly attached storage(DAS) is faster than any other storage methods. This is because it does not involve any overhead of data transfer over the network (all data transfer occurs on a dedicated connection between the server and the storage device. Mostly its Serially attached SCSI or SAS). However due to latest improvement's in fiber channel and other caching mechanism's, SAN also provides better speed's similar to DAS, and in some cases, it surpasses the speed provided by a DAS.

Before getting inside SAN, let's understand several media types and methods that are used to interconnect storage devices(when i say storage devices, please dont consider it as one single hard disk. Take it as an array of disk's, probably in some RAID level. Consider it as something like Dell's MD1200).

what is SAS(Serially Attached SCSI), FC(Fibre Channel), and iSCSI (Internet Small Computer System Interface)?


Traditionally the SCSI devices like the internal hard disk's are connected to a shared parallel SCSI bus. This means all devices attached, will be using the same bus to send/receive data.  But shared parallel connections are not good for high accuracy, and create issues during high speed transfers. However a serial connection between the device and the server can increase the overall throughput of the data transfer. SAS connections between storage devices and servers uses a dedicated 300 MB/Sec per disk. Think of SCSI bus that shares the same speed for all devices connected.



SAS uses the same SCSI commands to send and receive data from a device.  Also please do not think that SCSI is only used for internal storage. It is also used for external storage device to be connected to the server.



If data transfer performance and reliability is the choice, then using SAS is the best solution. In terms of reliability and error rate SAS disks are much better compared to the old SATA disks. SAS was designed by keeping performance in mind, due to which it is full-duplex. This means, data can be send and received simultaniously from a device using SAS. Also a single SAS host port can connect to multiple SAS drives using expanders. SAS uses point to point data transfer by using serial communication between devices (storage device, like disk drives & disk array's) and hosts.



The first generation of SAS provided around 3Gb/s of speed. The second generation of SAS improved this to 6Gb/s. And the third generation (which is currently used by many organization's for extremly high throughput) improved this to 12Gb/s.



Fiber Channel Protocol

Fiber Channel is a relatively new interconnection technology used for fast data transfer. The main purpose of its design is to enable transport of data at faster rates with a very less/negligible delay. It can be used to interconnect workstations, peripherals, storage array's etc.

The major factor that distinguishes fiber channel from other interconnecting method is that, it can manage both networking and I/O communication over a single channel using the same adapters.
ANSI (American National Standards Institute) standardized Fiber channel during 1988. When we say Fiber (in Fiber channel) do not think that it only supports optical fiber medium. Fiber is a term used for any medium used to interconnect in fiber channel protocol. You can even use copper wire for lower cost.

Please note the fact that fiber channel standard from ANSI supports networking, storage and data transfer. Fiber channel is not aware of the type of data that you transfer. It can send SCSI commands encapsulated inside a fiber channel frame(it does not have its own I/O commands to send and receive storage). The main advantage is that it can incorporate widely adopted protocols like SCSI and IP inside.


The components of making a fiber channel connection are mentioned below. The below requirement is very minimal to achieve a point to point connection. Typically this can be used for a direct connection between a storage array and a host.

An HBA (Host Bus Adapter) with Fiber channel port
Driver for the HBA card
Cables to interconnect devices in HBA fiber channel port

As mentioned earlier, SCSI protocol is encapsulated inside fiber channel. So normally SCSI data has to be modified to a different format that fiber channel can deliver to the destination. And when the destination receives the data it then retranslates it to SCSI.

You might be thinking that why do we need this mapping and re-mapping, why cant we directly use SCSI to deliver data. Its because SCSI cannot deliver data to greater distances to large number of devices (or large number of hosts).

Fiber cannel can be used to interconnect systems as far as 10KM (if used with optical fibers. You can increase this distance by having repeaters in between). And you can also transfer data to an extent of 30m using a copper wire for lower cost in fiber cannel.

With the emergence of fiber channel switches from variety of major vendors, connecting many large number of storage devices and servers have now become an easy task(provided you have the budget to invest). The networking ability of fiber channel led to the advanced adoption of SAN(Storage Area Networks) for faster, long distance, and reliable data access. Most of the high computing environment's(which requires fast and large volume data transfers) uses fiber channel SAN with optical fiber cables.

The current fiber channel standard (called as 16GFC) can transmit data  at the rate of 1600MB/s(dont forget the fact that this standard was released in 2011). The upcoming standards in the coming years are expected to provide  3200MB/s and 6400MB/s speed.

iSCSI(Internet Small Computer System Interface )



iSCSI is nothing but an IP based standard for interconnecting storage arrays and hosts. It is used to carry SCSI traffic over IP networks. This is the simplest and cheap solution(although not the best) to connect to a storage device.
This is a nice technology for location independent storage. Because it can establish connection to a storage device using local area networks, Wide area network. Its a Storage Area Network interconnection standard. It does not require special cabling and equipments like the case of a fiber channel network.
To the system using a storage array with iSCSI, the storage appears as a locally attached disk. This technology came after fiber channel and was widely adopted due to it low cost.

Its a networking protocol which is made on top of TCP/IP. You can guess that its not at all good performance wise, when compared with fiber channel(simply because everything is running over TCP with no special hardware and modifications to your architecture.)
iSCSI introduces a little bit of CPU load on the server, because the server has to do the extra processing for all storage requests over the network, with the regular TCP.

Related: Linux CPU performance Monitoring

iSCSI has the following disadvantages, compared to fiber channel



iSCSI introduces a little bit more latency compared to fiber channel, due to the overhead of IP headers
Database applications have small read and write operations, which when done on iSCSI will introduce more latency
iSCSI when done on the same LAN, which contains other normal traffic (other infrastructure traffic other than iSCSI), it will introduce a read/write lag or say low performance.
The maximum speed/bandwidth is limited to your ethernet and network speed. Even if you aggregate multiple links, it does not scal to the level of a fiber channel.
 NAS(Network Attached Storage)



The simplest definition of NAS is "Any server that shares its own storage with others on the network and acts as a file server is the simplest form NAS".

Please make a note of the fact that Network Attached Storage shares files over the network. Not storage device over the network.



NAS will be using an ethernet connection for sharing files over the network. The NAS device will have an IP address, and then will be accessible over the network through that IP address. When you access files on a file server on your windows system, its basically NAS.

The main difference is in how your computer or the server treats a particular storage. If the computer treats a storage as part of itself(similar to how you attach a DAS to your server), in other words, if the server's processor is responsible for managing the storage attached, it will be some sort of DAS. And if the computer/server treats the storage attached as another computer, which is sharing its data through the network, then its a NAS.



Directly attached storage(DAS) can be viewed as any other peripheral device like mouse keyboard etc. Because to the server/computer, its a directly attached storage device. However NAS is another server, or say an equipment having its own computing features that can share its own storage with others.



Even SAN storage can also be considered as an equipment that has its own processing/computing power. So the main difference between NAS, SAN and DAS is how the server/computer accessing it sees. A DAS storage device appears to the server as part of itself. The server sees it as its own physical part. Although the DAS storage device might not be inside the server(its normally another device with its own storage array), the server sees it as its own internal part(DAS storage appears to the server as its own internal storage)



When we talk about NAS, we need to call them shares rather than storage devices. Because NAS appears to a server as a shared folder instead of a shared device over the network. Please do not forget the fact that NAS devices are computers in themselves, who can share their storage space with others. When you share a folder with access control using SAMBA, its NAS.



Although NAS is a cheaper option for your storage needs. It really does not suit for an enterprise level high performance application. Never ever think of using a database storage (which needs to be high performing) with a NAS. The main downside of using NAS is its performance issue, and dependency on network(most of the times, the LAN which is used for normal traffic is also used for sharing storage with NAS, which makes it more congested)



Related: Linux Network Performance Tuning

Finally Discover The Function of the Human Appendix

For generations the appendix was thought to have no purpose. But now, researchers say they have discovered the true function of this organ, and it is anything but redundant.

Researchers now say that the appendix acts as a safe house for good bacteria. The body uses this to essentially “reboot” the digestive system when one suffers from a bout of dysentery or cholera.

Conventional wisdom used to claim that this small pouch protruding from the first part of the large intestine was simply redundant or an evolutionary shadow of a once useful organ. For years doctors advised people have their appendix removed and in spite of it’s now-apparent use, most seem none the worse for having it removed.

Duke University Medical Centre in North Carolina researchers say that following a severe bout of cholera or dysentery, which can purge the gut of bacteria essential for digestion, the appendix acts as a reserve for good bacteria to emerge.

In spite of the findings, Professor Bill Parker says that this does not mean we should cling onto our appendices at all costs.

“It’s very important for people to understand that if their appendix gets inflamed, just because it has a function it does not mean they should try to keep it in,” he explained.

“So it’s sort of a fun thing that we’ve found, but we don’t want it to cause any harm, we don’t want people to say, ‘oh, my appendix has a function’, so I’m not going to go to the doctor, I’m going to try to hang onto it.”

Nicholas Vardaxis, an associate professor in the Department of Medical Sciences at RMIT University, says that the theory put forward by the Duke University team makes a lot of sense.

“As an idea it’s an attractive one, that perhaps it would be a nice place for these little bacteria to localize in, a little cul-de-sac away from everything else,” he weighed in.

“The thing is that if we observe what’s been happening through evolution, the higher on the evolutionary scale we are and the more omnivorous animals become, then the smaller and less important the appendix becomes and humans are a good example of that.

“The actual normal flora bacteria within the appendix, as well within our gut, are the same, so we’ve lost all of those specialized bacteria.

“So it doesn’t have that safe house type of function anymore, I don’t think. 

“It’s a vestige of something that was there in previous incarnations, if you like.”

Scientists were led to the discovery by examining the appendices of koalas. Unlike the short human variety, the koala is famous for having an extremely long appendix.

This aids in their diet which is almost exclusively made up of eucalyptus leaves.

Professor Vardaxis says that in spite of the fact that the human appendix acts in a similar manner to that of koalas, it is unlikely that we will see a shrinking of the Australian marsupial’s organ any time soon.

“Unless of course we have a massive blight and we get the eucalypt on which the koala thrives dying, then we may find some mutant koalas out there perhaps that will start eating other things, and as they start to eat other things, then over generations and hundreds of thousands of years of time, then surely, yes, the koala’s appendix will shrink as well.”

Professor Vardaxis says that the human shrinkage of the appendix was due to changes in our diet that took place over many thousands of years. Still, it is possible that any species with a larger appendix now, could find themselves in a similar situation if their diet were to significantly change, and their appendix began to shrink. Koalas, Vardaxis explained, might be afflicted by appendicitis and have to have it taken out at times, just like humans.

Source: the collectiveint

If You Ever See Cracks In Your Watermelon

When You Cut It, Throw It Right Out. It Can Make You Sick

Bigger isn’t always better.

At least went it comes to watermelons, the summer treat that nearly everyone loves. The tasty fruit can be eaten in a variety of ways including: by the slice, as a smoothie addition and even as a way to sweeten up your salad. They are even used as a bowl for certain summery cocktail mixes where friend can gather around and soak up the sun while sipping through a straw. The growth of the fruit’s reputation has spiked, but in China, the growing fruit has had detrimental effects.

Unknown to China farmers, they had been using a fertilizer that contained a chemical called forchlorfenuron. The chemical has the power to expand the size of a watermelon by 20% at a more rapid pace, which ultimately leads to greater profits. At least that is what the fertilizer company thought.

When farmers had started to see their melons breaking in half and taking on a shape that was absent from their natural form, they were alerted. Even the taste and texture was altered from its original state. Farmers saw an abnormal amount of white seeds when the fruit normally contained mostly black seeds

The breaking in half of the watermelon was said to look like an explosion. While the chemical, which has been utilized since the early 1980s, is thought of as safe, Director of the Vegetable Research Institute at Qingdao Academy of Agricultural Science Cui Jian stated that it is best to veer away from plant hormone chemicals because watermelons are particularly sensitive to chemicals.

While the chemical used in the fertilizer seems to have the power to explode a watermelon, it has been confirmed that it is not harmful to health. The major downfall of the oversized fruit caused by the chemical is the watermelon may end up looking slightly abnormal and not many people have the room to store such a large food item that has a less-than-natural taste.

While Jian made his statement, the EPA (Environmental Protection Agency) countered it with an argument of their own. Also used in kiwis and grapes, the fertilizer is proven to be cytotoxic and can lead to acute dermal, oral and respiratory toxicity if ingested. While not carcinogenic, the substance contains toxins that can lead to bigger issues including increased fetal mortality and stomach lesions. Multiple tests have been completed on animals and proven to cause damage.

In addition to the toxin damage, the chemicals in the fertilizer can spread into the environment leading to damaging effects on our health that stem from the chemical blending with flora and fauna.

The Chinese government will continue to use its power to maintain an increase in food production, regardless of the poor effects on our health and the environment.

While the output of food is very important to the Chinese government, they offer a bit of hope in veering away from the toxin filled fertilizers and urge consumers to aim for organic fruit and vegetables.

WATCH : CHINA SINABING NABILI NA ANG ILANG BAHAGI NANG PINAS NUNG SI CORY PA ANG PANGULO

The South China Sea is a marginal sea that is part of the Pacific Ocean, encompassing an area from the Karimata and Malacca Straits to the Strait of Taiwan of around 3,500,000 square kilometresPresident Xi Jinping seems to agree with the Athenian general who, more than 2,000 years ago, warned the people of Melos that  the strong do what they wish and the weak do as they are compelled. His government insists that nearly all the South China Sea belongs to China—even islets and reefs close to the Philippines and five other littoral states but hundreds of miles from the Chinese mainland. Instead of raising China in harmony, Beijing’s policies point the world toward the brink of war. Intransigent, Beijing rejects the jurisdiction of the Permanent Court of Arbitration and its ruling that China has no historic rights to large swathes of the South China Sea and has wrongly abused not only fishing vessels from the Philippines but the coral riches beneath the water. 
Skeptics about international law say that China behaves no differently from other great powers. Few, if any, have bowed to international tribunals. When Nicaragua complained that the United States was mining its waters, the Reagan administrations simply discarded the U.S. commitment to accept compulsory jurisdiction of the International Court of Justice and rejected the court’s ruling in 1986 against the United States. In a similar vein,  the George W. Bush administration “un-signed” the statute creating the International Criminal Court and abrogated, with no legal justification, the Nixon administration’s treaty with Moscow limiting ballistic missile defense.While the UN Charter bans acts of aggression,  China’s seizure and militarization of islands and reefs in the South China Sea do not directly violate this standard. Still, China’s actions (along with Russia’s in the Caucasus and Ukraine) do breach the principle enunciated by the U.S. Secretary of State Henry Stimson  in 1932. Responding to Japan’s invasion of Manchuria, Stimson declared that the United States would not recognize any political or territorial changes accomplished by force. Though not a member of the League of Nations, a U.S. representative joined the League’s investigation of Japan’s puppet state “Manchukuo.” The League said it would not recognize the new state of Manchukuo on the grounds that its establishment violated the territorial integrity of China, and therefore the Nine-Power Treaty to which many prominent league members subscribed. Neither the Stimson Doctrine nor the League’s declaration stopped  Japan’s invasion of China. Still,  Stimson’s key principle had greater effect when the Soviet Union invaded and  absorbed Estonia, Latvia, and Lithuania in 1940. Even though Washington and its allies came to value Stalin as an ally against Hitler, none recognized Moscow’s annexation of the Baltic states.  Indeed, the three Baltic countries retained their embassies in Washington for five decades. Upholding the Stimson principle helped to delegitimize Soviet occupation and enable Estonians, Latvians, and Lithuanians to reestablish their independence in 1990-1991.Enjoying this article?Taking a leaf from Thucydides on the root cause of the Peloponnesian War, some analysts warn that China and the United States are destined to fight. Indeed, Michael Pillsbury argues that  China’s elites are engaged in a hundred-year marathon to displace the United States as global leader. China’s actions in the South China Sea and elsewhere seem to confirm the expectation that rising powers will challenge the existing order and its dominant power.

FLAKKA - New killer synthetic drugs

In the Philippines, the government under President Duterte has recently declared an all out war against drugs, however, in different countries around the world, drug manufacturers are even producing new synthetic drugs that could catch the attention of the consumers.

Now, most of us believe that zombies don't exist and that they only appear in movies and tv series, however, with the newest drug in the US, people have been witnessing how a human slowly acts like a zombie! 

The newest drug called 'Flakka Drug' is a synthetic street drug that makes a human act like a zombie. In 2014, the rug was reported to have these effects: bizarre behavior, agitation, paranoia, and delusions of superhuman strength.

There are already lots of reported cases involving this drug like a man runnng naked through a traffic, an addict who attemtped to do IT