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Ip san-data-storage-for-media-applications
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Ip san-data-storage-for-media-applications


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While, traditionally the media firms have looked to DAS or Fibre Channel (FC) based SAN for storage of digital media for various reasons, IP SAN technologies are fast becoming cost-effective and …

While, traditionally the media firms have looked to DAS or Fibre Channel (FC) based SAN for storage of digital media for various reasons, IP SAN technologies are fast becoming cost-effective and competitive technology to replace them.

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  • 1. IP SAN Data Storage for Media ApplicationsIntroductionDigitization of data is one of the key drivers of the media and entertainment industry in India accordingto a recent FICCI-KPMG report. Replacing the over 50 year old analog technology, digital transmissionand storage of media bring improved communication, security, quality and flexibility to the table. While,traditionally the media firms have looked to DAS or Fibre Channel (FC) based SAN for storage of digitalmedia for various reasons, IP SAN technologies are fast becoming cost-effective and competitivetechnology to replace them.Quality of ServiceMedia applications are bandwidth-intensive technologies that place high demands on the storagesubsystem in comparison to traditional file serving and online transaction processing (OLTP) storage.While OLTP loads are typically random loads that are drive limited and do not saturate the links, mediaapplications such as CCTV and media broadcasting applications have one or more audio and videostreams that demand specific data transfer rates that must be met to satisfy Quality of Service (QoS)requirements.In the case of audio/video streaming applications, QoS refers to the need that the user must receive theaudio/video without interruption and loss of quality by lost frames. In order to keep the media streamcontinuous, often, some type of buffering is implemented to eliminate the effects of kinks in the line.The user’s experience of uninterrupted reception can be guaranteed only if the buffer is maintained tobe non-empty at any time. One way of ensuring continuous playback is by dropping intermittent framesthereby reducing the frame rate. However, this would result in loss of audio/video quality. With themodern day demands of high definition video and audio, this would not be an acceptable solution.Another way to ensure a continuous playback in such a scenario is to have a bigger buffer therebymitigating the effect of slower links. Thus it becomes clear that the rate of the incoming streams (link)play a big role providing the required quality of service. This depends on both the link available and theability of the storage to deliver the required throughput (data transfer rate).Likewise, for CCTV type of applications when different parts of a surveillance area are monitored usingmany recording cameras and monitors, there are a number of recording and playback streamshappening simultaneously to and from the storage. These parallel streams place high demands onthroughputs from the storage.
  • 2. Storage approachesTraditionally, such setups have a local storage attached to the cameras, thereby avoiding any link delays.However, such distributed Direct Attached Storage (DAS) are inefficient means of allocating, using andscaling storage. Storage consolidation with SAN and NAS storage solutions address these concerns offlexibility and scalability by centralizing the storage for all recording and playback streams. However, thiswould mean that the bandwidth of the links play a critical role in deciding the throughputs achievable.Thus far, Fibre Channel based SAN with their 4Gbps throughputs have been favored over IP SAN andNAS solutions with traditionally much lower throughputs. However, the costs of setting up a FibreChannel network remain expensive and include an elaborate setup of equipment not commonlyavailable in enterprises including Fibre channel adapters and switches.Ethernet based IP SAN solutions work with the existing LAN networks available in the enterprises,thereby increasing the ease of installation and reducing the acquisition costs. However, until recently, IPSAN solutions using iSCSI have been confined to file serving or OLTP type of applications that typically donot need high throughputs. But, when it comes to bandwidth-intensive applications such as mediaapplications the throughput assumes critical significance. With gigabit Ethernet (GigE) ports used forcommercial iSCSI storage solutions, data transfer rates of 1Gbps or about 125 MB/s (half-duplex) or over200 MB/s (full-duplex) can be achieved. But, this is significantly lower than the rates achievable fromfibre channel links. For these reasons, and reasons of relative newness of iSCSI, Fibre Channel basedstorage solutions have been preferred thus far for media applications. However, of late, with the influxof several key technologies and performance improvements, IP SAN solutions have gained acceptance inthe media industry.Benefits of iSCSIiSCSI built on top of the erstwhile SCSI (Small Computer System Interface) works by transmitting SCSIpackets using TCP and IP protocols that offer services such as guaranteed delivery, flow control andaddressing. Since TCP/IP are the ubiquitous transport and network protocol layers of Ethernet networksand the Internet, iSCSI storage solutions can co-exist with existing networks in the enterprise makingthem easy to setup and administer and without the need for specialized hardware lowers the overallstorage costs.Today, a number of vendors offer a spectrum of robust and scalable and iSCSI based storage solutionsthat include advanced SAN feature sets that mirror the feature sets of FC SAN solutions. Severaladvanced features such as Thin Provisioning, Snapshots, Synchronous and asynchronous replication, HAClusters and Clustering, CDP etc are available in iSCSI based storage solutions as well. In fact, certainfeatures such as asynchronous replication that needs to operate over long distances benefit from iSCSIstorage that work with the omnipresent Ethernet networks when compared to distance limited FC
  • 3. setups. Storage solutions such as AMI’s StorTrends iTX have in-built WAN acceleration techniques thathelp in speeding up the data replication throughputs to near-bandwidth level.Thus, concerns about reliability and stability of iSCSI solutions have been answered. This is apparentfrom an Enterprise Strategy Group (ESG) survey couple of years ago that found that 50% of iSCSIapplications are Tier-1 application primary storage and 36% of the implementations had used iSCSI fortheir application primary data. These numbers are on the rise and iSCSI will continue to take a biggershare of the exploding storage market.iSCSI Performance – Numbers MatterAn (ESG) Lab report from 5 years ago has indicated that the difference in FC and iSCSI performance isvery minimal (about 5-16% depending on the application including bandwidth-hungry applications suchas media applications) and a carefully crafted iSCSI setup can outperform FC setups. An eye-openingstatistic in this ESG Lab Report was that a large amount of FC infrastructure deployments were inproduction environments that were still 1 Gb. This goes to show that the performance level offered byGigE based iSCSI storage solutions would have been sufficient for these deployments. Since the labreport was published both FC and iSCSI have had several improvements made towards improving theirperformance. Several key performance improvement techniques can be done to improve theperformance of iSCSI storage solutions. These include –Advanced Caching techniquesCaching is a critical component in storage systems. A carefully designed caching architecture would go along way in improving the performance of iSCSI storage solutions. By selecting a kernel based iSCSI stackthat integrates with the caching module in such a way that it ensures that there is zero memory copyinvolved thereby placing less demands on the system resources such as CPU and memory and ensurethat the system performs with enough steam left to handle much more loads. iSCSI storage solutions,such as the StorTrends storage servers from American Megatrends Inc (AMI), also tune the cachinggranularities based on the underlying block sizes, which includes the RAID stripe size, thereby helping toautomatically tuning the disk spindles to yield the best possible I/O performance. In addition, for mediaapplications whose IO load patterns are sequential in nature reading blocks ahead using Read-aheadCaching mode would minimize the number of disk IOs, thereby drawing the best performance from thesystem.Multipathing and Network TeamingStorage solutions such as AMI’s StorTrends iTX support multiple connections to the same target from aninitiator, meaning multiple GigE links can communicate with the same target. Thus using MPIO(Multipath IO) and network aggregation and virtualization techniques where multiple NICs are
  • 4. abstracted as a single interface having higher bandwidth will ensure that the throughput achieved forsequential loads of a media application can match or exceed the throughputs of FC by balancing theloads across multiple links and concurrent transport utilization.Initiator CPU tuningOne of the precepts for favoring iSCSI over FC is the minimal requirements on the host side and the easeof setup. In order to do this, software iSCSI initiators are often used to connect to the iSCSI target andprovide a virtual block device on the host side. However, one of the concerns raised by critics of iSCSI isthat this would mean higher CPU utilization in the host causing applications to slow down.iSCSI was designed to work over Ethernet, which was devised for small packets in the range of 1.5 KB.The general line of thinking is that since more packets mean more interrupts and, by extension, moreCPU overhead, iSCSI would seem to be at a disadvantage here. By offering the support for jumbo framesizes of up to 9KB in size, iSCSI storage servers adequately address this issue, allowing for enhanced I/Operformance and lower CPU utilization. Conversely, if the CPU becomes an issue on the server side, thenan iSCSI Host Bus Adapter can also be used to increase performance.10 GbE and FCoEDespite the vast performance improvements offered by iSCSI today the hard core critics of iSCSI remainunmoved. iSCSI addresses these concerns and steps to the next level with the arrival of 10 GigabitEthernet exceeding bandwidths offered by FC. Offering 10 times the bandwidth offered by the current 1Gbps offerings, the throughputs of iSCSI solutions grow manifold satisfying even the most bandwidth-hungry media applications.While the gap to the performance has been bridged by the iSCSI industry, now there is a growing needfor both these technologies to coexist. Often, enterprises, who have already adopted Fibre Channel,now seek to use iSCSI but do not want to get rid of their already spent money and time on build the FCsetup. Fiber Channel over Ethernet (FCoE), an encapsulation of Fiber Channel frames over Ethernet, isaimed at bridging this gap.ConclusionMedia applications are bandwidth-hungry applications that place high demands on the Quality ofService obtained from the underlying storage. Initially favoring DAS and FC SAN solutions, now theseapplications have started moving towards iSCSI based storage solutions. ISCSI based storage solutionshave now stabilized and offer any and every service that FC offers and have started eating in to themarket space that was previously dominated by FC based solutions.For More Information about IP SAN Storage Solutions ,