Tape Storage Research Articles

RS-LDPC Concatenated Coding for the Modern Tape Storage Channel

In modern tape storage, user data are recorded and retrieved along multiple tracks of rapidly moving, flexible magnetic medium that give rise to a variety of channel impediments including occasional long erasures, more frequent amplitude fades as well as a large amount of random errors. This work considers reliable recovery of data from such tape channels using a novel concatenation of an inner Reed-Solomon (RS) code and an outer nonbinary low-density parity-check (LDPC) code. This particular concatenation scheme and a highly tailored iterative decoding algorithm are chosen to efficiently handle the assortment of the tape channel impediments while meeting the stringent target error rate constraint as well as key practical requirements of the mass tape storage system. Despite the use of a nonbinary LDPC code, the proposed scheme allows excellent performance-complexity tradeoffs. In stark contrast to any existing coding schemes that involve LDPC codes, the proposed concatenation strategy allows semianalytic error rate performance evaluation at rates below what is possible using modern computers, thus providing an ability to ensure satisfactory low-error-rate performance.

The Use of Adhesive Tapes to Transfer Skin-scrapings for Sequential Laboratory Diagnosis of Dermatophytosis.

Dermatophytosis usually causes a skin problem, which requires both clinical findings and laboratory investigations for diagnosis. Whereas, fungal culture is considered as the gold standard procedure, it is more difficult to perform compared to potassium hydroxide（KOH）examination. To evaluate the efficacy of KOH and fungal culture examinations from skin-scraping specimens, which were kept in transparent adhesive tapes at different time intervals. Skin-scraping specimens were collected from clinically suspected cases by conventional technique using scalpel blades and kept using transparent adhesive tapes. KOH（10%）preparation and fungal cultures were then performed by highly experienced technicians at different time intervals: day 0（the day of specimen collection, which was set as the standard reference point）, day 3 or 4, day 7, day 14, and day 28. Thereafter, the yield for detection of fungal elements by KOH examination and positive fungal cultures from specimens stored in adhesive tape was determined at different time intervals and compared to the results from the standard reference point. The sensitivity of KOH exami-nations from 162 patients at different time intervals showed no significant difference when compared to the standard reference point at day 0. In contrast, the sensitivity of fungal culture progressively decreased as the storage period was prolonged. KOH examination of skin-scrapings from the adhesive tape storage technique yield good results even when specimens have been kept up to one month. On the other hand, the sensitivity of fungal cultures gradually declines as storage time is extended.

Near-optimal tape transport control with feedback of velocity and tension

Abstract: With the increasing recording areal density and volumetric density targeted by magnetic tapes, high-performance tape transport is of fundamental importance to achieve the required reliability in tape storage systems. In this paper, the time-varying characteristics of tape transport are taken into account to design a velocity and tension feedback control system using p-type controllers that depend on the longitudinal tape position. Analytical expressions are given for the controller gains, for which all transfer functions become essentially independent of longitudinal position. Experimental results are presented for a tape system where feedback of tension is provided by a tension sensing roller.

Recent Evolution of the Offline Computing Model of the NOvA Experiment

The NOvA experiment at Fermilab is a long-baseline neutrino experiment designed to study νe appearance in a νμ beam. Over the last few years there has been intense work to streamline the computing infrastructure in preparation for data, which started to flow in from the far detector in Fall 2013. Major accomplishments for this effort include migration to the use of off-site resources through the use of the Open Science Grid and upgrading the file-handling framework from simple disk storage to a tiered system using a comprehensive data management and delivery system to find and access files on either disk or tape storage. NOvA has already produced more than 6.5 million files and more than 1 PB of raw data and Monte Carlo simulation files which are managed under this model. The current system has demonstrated sustained rates of up to 1 TB/hour of file transfer by the data handling system. NOvA pioneered the use of new tools and this paved the way for their use by other Intensity Frontier experiments at Fermilab. Most importantly, the new framework places the experiment's infrastructure on a firm foundation, and is ready to produce the files needed for first physics.

Pooling the resources of the CMS Tier-1 sites

The CMS experiment at the LHC relies on 7 Tier-1 centres of the WLCG to perform the majority of its bulk processing activity, and to archive its data. During the first run of the LHC, these two functions were tightly coupled as each Tier-1 was constrained to process only the data archived on its hierarchical storage. This lack of flexibility in the assignment of processing workflows occasionally resulted in uneven resource utilisation and in an increased latency in the delivery of the results to the physics community.The long shutdown of the LHC in 2013-2014 was an opportunity to revisit this mode of operations, disentangling the processing and archive functionalities of the Tier-1 centres. The storage services at the Tier-1s were redeployed breaking the traditional hierarchical model: each site now provides a large disk storage to host input and output data for processing, and an independent tape storage used exclusively for archiving. Movement of data between the tape and disk endpoints is not automated, but triggered externally through the WLCG transfer management systems.With this new setup, CMS operations actively controls at any time which data is available on disk for processing and which data should be sent to archive. Thanks to the high-bandwidth connectivity guaranteed by the LHCOPN, input data can be freely transferred between disk endpoints as needed to take advantage of free CPU, turning the Tier-1s into a large pool of shared resources. The output data can be validated before archiving them permanently, and temporary data formats can be produced without wasting valuable tape resources. Finally, the data hosted on disk at Tier-1s can now be made available also for user analysis since there is no risk any longer of triggering chaotic staging from tape.In this contribution, we describe the technical solutions adopted for the new disk and tape endpoints at the sites, and we report on the commissioning and scale testing of the service. We detail the procedures implemented by CMS computing operations to actively manage data on disk at Tier-1 sites, and we give examples of the benefits brought to CMS workflows by the additional flexibility of the new system.

Data preservation at the Fermilab Tevatron

The Fermilab Tevatron collider's data-taking run ended in September 2011, yielding a dataset with rich scientific potential. The CDF and DO experiments each have nearly 9 PB of collider and simulated data stored on tape. A large computing infrastructure consisting of tape storage, disk cache, and distributed grid computing for physics analysis with the Tevatron data is present at Fermilab. The Fermilab Run II data preservation project intends to keep this analysis capability sustained through the year 2020 or beyond. To achieve this, we are implementing a system that utilizes virtualization, automated validation, and migration to new standards in both software and data storage technology as well as leveraging resources available from currently-running experiments at Fermilab. These efforts will provide useful lessons in ensuring long-term data access for numerous experiments throughout high-energy physics, and provide a roadmap for high-quality scientific output for years to come.

A Study of Timing Recovery for High-Recording-Density Tape Systems

Today's tape storage systems are widely used as a low-cost solution for data backup and archiving for the rapidly growing amount of digital information produced in various fields. Following the Information Storage Industry Consortium (INSIC) Roadmap [1], tape cartridge capacity continues to scale by doubling the capacity every two years. Developments in read channel technology are expected to play an important role in improving data-storage capability. The introduction of powerful error-correction codes, such as low density parity check (LDPC) codes to the tape storage system (and which have already been applied to current HDD systems) is anticipated to achieve system operation under low SNR conditions, enabling additional increases in areal recording density. However, at a low SNR, a loss-of-lock (LOL) in the phase-locked loop (PLL) will frequently occur in the current timing recovery scheme. Previous studies of the iterative timing recovery scheme [2], [3] enable systems to operate robustly even at low SNR conditions. However, due to the complexity of these systems, the cost of hardware makes it difficult to introduce iterative timing recovery schemes into multichannel tape systems. In this work, it is shown that erroneous feedback in the PLL caused by misdetection of the detector is the major cause for LOL in tape systems at high recording densities. To cope with these misdetections of the detector while maintaining an acceptable latency in the feedback loop, a new timing recovery scheme that utilizes the soft-output information of the detector was studied. The results show that LOL rate performance can clearly be improved by such schemes, with only a small increase in implementation complexity.

Asymmetrically Wrapped Flat-Profile Tape–Head Friction and Spacing

In this work, we study the friction and spacing between a magnetic data storage tape and a recording head. The tape–head friction force and magnetic spacing are measured as a function of the angles with which the tape is wrapped around the read/write head at 2 and 6 m s−1 tape transport velocity. It is found that the friction force can be described as a linear function of the leading and trailing wrap angles, where the friction force increases for increasing wrap angles. The analysis treats the total friction force as the sum of three components resulting from (1) the leading edge, (2) the head surface, and (3) the trailing edge. Coefficients of friction are calculated for each of the three components from experimental data. The leading edge and head surface components are both dependent on the leading-edge wrap angle and independent of the trailing-edge wrap angle, whereas the trailing-edge component is only dependent on the trailing-edge wrap. In addition, the estimated magnetic spacing is found to decrease with increasing leading-edge wrap angle, but is independent of the trailing-edge wrap angle, even for negative trailing-edge wrap angles. Hence, the trade-off between friction and spacing can be optimized through judicious choice of the wrap angles. In addition, we find that a significant portion of the friction is due to edge friction (as high as 70 % in the case of symmetric wrap). Therefore, we conclude that modifications to the head surface topography to reduce the contact area may not result in a significant reduction in head–tape friction.

A self-configuring control system for storage and computing departments at INFN-CNAF Tierl

The storage and farming departments at the INFN-CNAF Tier1[1] manage approximately thousands of computing nodes and several hundreds of servers that provides access to the disk and tape storage. In particular, the storage server machines should provide the following services: an efficient access to about 15 petabytes of disk space with different cluster of GPFS file system, the data transfers between LHC Tiers sites (Tier0, Tier1 and Tier2) via GridFTP cluster and Xrootd protocol and finally the writing and reading data operations on magnetic tape backend. One of the most important and essential point in order to get a reliable service is a control system that can warn if problems arise and which is able to perform automatic recovery operations in case of service interruptions or major failures. Moreover, during daily operations the configurations can change, i.e. if the GPFS cluster nodes roles can be modified and therefore the obsolete nodes must be removed from the control system production, and the new servers should be added to the ones that are already present. The manual management of all these changes is an operation that can be somewhat difficult in case of several changes, it can also take a long time and is easily subject to human error or misconfiguration. For these reasons we have developed a control system with the feature of self-configure itself if any change occurs. Currently, this system has been in production for about a year at the INFN-CNAF Tier1 with good results and hardly any major drawback. There are three major key points in this system. The first is a software configurator service (e.g. Quattor or Puppet) for the servers machines that we want to monitor with the control system; this service must ensure the presence of appropriate sensors and custom scripts on the nodes to check and should be able to install and update software packages on them. The second key element is a database containing information, according to a suitable format, on all the machines in production and able to provide for each of them the principal information such as the type of hardware, the network switch to which the machine is connected, if the machine is real (physical) or virtual, the possible hypervisor to which it belongs and so on. The last key point is a control system software (in our implementation we choose the Nagios software), capable of assessing the status of the servers and services, and that can attempt to restore the working state, restart or inhibit software services and send suitable alarm messages to the site administrators. The integration of these three elements was made by appropriate scripts and custom implementation that allow the self-configuration of the system according to a decisional logic and the whole combination of all the above-mentioned components will be deeply discussed in this paper.

Unlocking the Australian Landsat Archive – From dark data to High Performance Data infrastructures

Earth Observation data acquired by the Landsat missions are of immense value to the global community and constitute the world’s longest continuous civilian Earth Observation program. However, because of the costs of data storage infrastructure these data have traditionally been stored in raw form on tape storage infrastructures which introduces a data retrieval and processing overhead that limits the efficiency of use of this data. As a consequence these data have become ‘dark data’ with only limited use in a piece-meal and labor intensive manner. The Unlocking the Landsat Archive project was set up in 2011 to address this issue and to help realize the true value and potential of these data.The key outcome of the project was the migration of the raw Landsat data that was housed in tape archives at Geoscience Australia to High Performance Data facilities hosted by the National Computational Infrastructure (a super computer facility located at the Australian National University). Once this migration was completed the data were calibrated to produce a living and accessible archive of sensor and scene independent data products derived from Landsat-5 and Landsat-7 data for the period 1998–2012. The calibrated data were organized into High Performance Data structures, underpinned by ISO/OGC standards and web services, which have opened up a vast range of opportunities to efficiently apply these data to applications across multiple scientific domains.

Long term stabilities of magnetic tape for data storage in office environment

The long-term stability of magnetic particulate tapes was investigated using two formats of metal data cartridge tapes for data backup, both of which had been stored in a typical office environment for more than a decade. A more modern barium ferrite data cartridge tape was also used. Analysis by a vibrating sample magnetometer, surface roughness analyzer and friction tester were used to ascertain the magnetic and tribological properties, while gel permeation chromatography, gas chromatography were employed to analyze the stability of organic materials such as binder polymers and lubricants. The magnetic and tribological performance remained stable. Moreover, the degradation of organic materials was found to be less in the data cartridge tapes that were launched after the 2000s, including the more modern barium ferrite data cartridge tapes. These results confirm the long-term stability of data cartridge tapes, indicating a longevity that is in excess of 25 years.

Durable ultrathin silicon nitride/carbon bilayer overcoats for magnetic heads: The role of enhanced interfacial bonding

Pole tip recession (PTR) is one of the major issues faced in magnetic tape storage technology, which causes an increase in the magnetic spacing and hence signal loss during data readback. Despite efforts to reduce the magnetic spacing, PTR, and surface wear on the heads by using protective overcoats, most of them either employ complex fabrication processes and approaches do not provide adequate protection to the head or are too thick (∼10–20 nm), especially for future high density tape storage. In this work, we discuss an approach to reduce the PTR and surface wear at the head by developing an ultrathin ∼7 nm bilayer overcoat of silicon/silicon nitride (Si/SiNx) and carbon (C), which is totally fabricated by a cost-effective and industrial-friendly magnetron sputtering process. When compared with a monolithic C overcoat of similar thickness, the electrically insulating Si/SiNx/C bilayer overcoat was found to provide better wear protection for commercial tape heads, as demonstrated by Auger electron spectroscopic analyses after wear tests with commercial tape media. Although the microstructures of carbon in the monolithic and bilayer overcoats were similar, the improved wear durability of the bilayer overcoat was attributed to the creation of extensive interfacial bonding of Si and N with the C overcoat and the alumina-titanium carbide composite head substrate, as predicted by time-of-flight secondary ion mass spectrometry and confirmed by in-depth X-ray photoelectron spectroscopy analyses. This study highlights the pivotal role of enhanced interfaces and interfacial bonding in developing ultrathin yet wear-durable overcoats for tape heads.

Rewinding tape tech

It might not have the glamour it used to, but tape storage is still a force

A gap in patient tape storage and use practices puts patients at risk for cutaneous fungal infections

We report a case of a cutaneous fungal infection in a 12-year-old oncology patient related to patient tape. Our facility had no established guidelines for patient tape. A survey conducted of multiple local healthcare facilities revealed no existing policies or standards of care related to tape storage or use. This reveals a gap in practice. We call for formal recommendations for tape storage and use to enhance patient safety.

Archiving and Managing Remote Sensing Data using State of the Art Storage Technologies

Abstract. Integrated Multi-mission Ground Segment for Earth Observation Satellites (IMGEOS) was established with an objective to eliminate human interaction to the maximum extent. All emergency data products will be delivered within an hour of acquisition through FTP delivery. All other standard data products will be delivered through FTP within a day. The IMGEOS activity was envisaged to reengineer the entire chain of operations at the ground segment facilities of NRSC at Shadnagar and Balanagar campuses to adopt an integrated multi-mission approach. To achieve this, the Information Technology Infrastructure was consolidated by implementing virtualized tiered storage and network computing infrastructure in a newly built Data Centre at Shadnagar Campus. One important activity that influences all other activities in the integrated multi-mission approach is the design of appropriate storage and network architecture for realizing all the envisaged operations in a highly streamlined, reliable and secure environment. Storage was consolidated based on the major factors like accessibility, long term data protection, availability, manageability and scalability. The broad operational activities are reception of satellite data, quick look, generation of browse, production of standard and valueadded data products, production chain management, data quality evaluation, quality control and product dissemination. For each of these activities, there are numerous other detailed sub-activities and pre-requisite tasks that need to be implemented to support the above operations. The IMGEOS architecture has taken care of choosing the right technology for the given data sizes, their movement and long-term lossless retention policies. Operational costs of the solution are kept to the minimum possible. Scalability of the solution is also ensured. The main function of the storage is to receive and store the acquired satellite data, facilitate high speed availability of the data for further processing at Data Processing servers and help to generate data products at a rate of about 1000 products per day. It also archives all the acquired data on tape storage for long-term retention and utilization. Data sizes per satellite pass range from hundreds of megabytes to tens of gigabytes The images acquired from remote sensing satellites are valuable assets of NRSC and are used as input for further generation of different types of user data products through multiple Data Processing systems. Hence, it is required to collect and store the data within a shared, high speed repository concurrently accessible by multiple systems. After the raw imagery is stored on a high-speed repository, the images must be processed in order for them to be useful for value-added processing or for imagery analysts. The raw image file has to be copied on to data processing servers for further processing. Given the large file sizes, it is impractical to transfer these files to processing servers via a local area network. Even at gigabit Ethernet rates (up to 60 MB/s), a 5 GB file will take at least 83 seconds. For this reason, it is useful to employ a shared file system which allows every processing system to directly access the same pool where raw images were stored. Concurrent access by multiple systems is ensured for processing and generation of data products. With the above reasons, it was chosen to have high speed disk arrays for acquisition and processing purposes and tape based storage systems for long-term huge data (Peta Bytes) archival in a virtualized multitier storage architecture. This paper explains the architecture involved in a virtualized tiered storage environment being used for acquisition, processing and archiving the remote sensing data. It also explains the data management aspects involved in ensuring data availability and archiving Peta bytes sized, remote sensing data acquired over the past 40 years.

MICE data handling on the Grid

The international Muon Ionisation Cooling Experiment (MICE) is designed to demonstrate the principle of muon ionisation cooling for the first time, for application to a future Neutrino factory or Muon Collider. The experiment is currently under construction at the ISIS synchrotron at the Rutherford Appleton Laboratory (RAL), UK. In this paper we present a system – the Raw Data Mover, which allows us to store and distribute MICE raw data – and a framework for offline reconstruction and data management. The aim of the Raw Data Mover is to upload raw data files onto a safe tape storage as soon as the data have been written out by the DAQ system and marked as ready to be uploaded. Internal integrity of the files is verified and they are uploaded to the RAL Tier-1 Castor Storage Element (SE) and placed on two tapes for redundancy. We also make another copy at a separate disk-based SE at this stage to make it easier for users to access data quickly. Both copies are check-summed and the replicas are registered with an instance of the LCG File Catalog (LFC). On success a record with basic file properties is added to the MICE Metadata DB. The reconstruction process is triggered by new raw data records filled in by the mover system described above. Off-line reconstruction jobs for new raw files are submitted to RAL Tier-1 and the output is stored on tape. Batch reprocessing is done at multiple MICE enabled Grid sites and output files are shipped to central tape or disk storage at RAL using a custom File Transfer Controller.

A data handling system for modern and future Fermilab experiments

Current and future Fermilab experiments such as Minerva, NOνA, and MicroBoone are now using an improved version of the Fermilab SAM data handling system. SAM was originally used by the CDF and D0 experiments for Run II of the Fermilab Tevatron to provide file metadata and location cataloguing, uploading of new files to tape storage, dataset management, file transfers between global processing sites, and processing history tracking. However SAM was heavily tailored to the Run II environment and required complex and hard to deploy client software, which made it hard to adapt to new experiments. The Fermilab Computing Sector has progressively updated SAM to use modern, standardized, technologies in order to more easily deploy it for current and upcoming Fermilab experiments, and to support the data preservation efforts of the Run II experiments.

Operating the Worldwide LHC Computing Grid: current and future challenges

The Wordwide LHC Computing Grid project (WLCG) provides the computing and storage resources required by the LHC collaborations to store, process and analyse their data. It includes almost 200,000 CPU cores, 200 PB of disk storage and 200 PB of tape storage distributed among more than 150 sites. The WLCG operations team is responsible for several essential tasks, such as the coordination of testing and deployment of Grid middleware and services, communication with the experiments and the sites, followup and resolution of operational issues and medium/long term planning. In 2012 WLCG critically reviewed all operational procedures and restructured the organisation of the operations team as a more coherent effort in order to improve its efficiency. In this paper we describe how the new organisation works, its recent successes and the changes to be implemented during the long LHC shutdown in preparation for the LHC Run 2.

The GridKa Tier-1 Computing Center within the ALICE Grid Framework

The GridKa computing center, hosted by Steinbuch Centre for Computing at the Karlsruhe Institute for Technology (KIT) in Germany, is serving as the largest Tier-1 center used by the ALICE collaboration at the LHC. In 2013, GridKa provides 30k HEPSPEC06, 2.7 PB of disk space, and 5.25 PB of tape storage to ALICE. The 10Gbit/s network connections from GridKa to CERN, several Tier-1 centers and the general purpose network are used by ALICE intensively. In 2012 a total amount of ~1 PB was transferred to and from GridKa. As Grid framework, AliEn (ALICE Environment) is being used to access the resources, and various monitoring tools including the MonALISA (MONitoring Agent using a Large Integrated Services Architecture) are always running to alert in case of any problem. GridKa on-call engineers provide 24/7 support to guarantee minimal loss of availability of computing and storage resources in case of hardware or software problems. We introduce the GridKa Tier-1 center from the viewpoint of ALICE services.

Structured and Unstructured Data Retention Solution

Data Retention solutions are increasingly important as the world becomes more digital. These solutions help museums, national libraries, governments, educational institutions, and corporations world-wide capture and manage institutional assets. Data Retention provides a means of organizing institutional data while providing greater levels of access and controls.Today's Data Retention solutions must be extensible to meet the evolving business needs of Big Data and Cloud Computing. While Hierarchical Storage Solutions and tiered storage provide the most reliable and cost effective solution, access and performance requirements are also important design factors. If architected incorrectly, data searching and retrieval can be time consuming and costly. Traditional tape-only archival methods simply do not meet the access requirements of many of today's repositories and long-term archives. Likewise, storing all the data on disk requires greater administration and is more costly. The proposed Data Retention solution provides a proven solution with a balance between disk, tape, and cloud storage to support long term archiving of structured and unstructured data.