April Figure 1. SEM image of tape using MP particles. Figure 2. SEM image of tape using BaFe particles

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1 April 2013 ABSTRACT The latest and sixth generation of Linear Tape Open (LTOTM) technology introduces two magnetic pigment particle options for users of tape. The two particle options include Metal Particulates (MP) and Barium Ferrite (BaFe). The physical properties of these two types of particles have their own benefits which create slight differences in tape technology performance and data longevity. This paper will uncover in-depth the various properties and benefits of both LTO6 MP and BaFE particles and demonstrate that both particles fully meet strict LTO data cartridge requirements. INTRODUCTION An LTO6 data cartridge provides 2.5 terabytes (TB) of native capacity in a single cartridge. The cartridge has 846 meters of half-inch wide tape wound onto a single spool/reel. The head in the drive has 16 channels that are all active at the same time providing a continuous data rate of 160 megabytes/second. There are 2,176 longitudinal data tracks across the half-inch tape and the data is stored at a density of about 15,000 bits per millimeter. Due to the high track density on the tape, all LTO formats use servo tracks for positional feedback to keep the read/write head aligned with the data tracks during operation. These servo tracks are written at a lower density than the data tracks and are significantly larger than the data tracks. There are five servo tracks spaced evenly across the width of the half-inch tape. LTO6 MP OR BaFe: WHAT S THE DIFFERENCE? The magnetic properties of tape derive from the type of magnetic pigment particles used in the tape. These pigment particles are very small (20-40 nanometers across their largest dimensions) and have very specific magnetic properties. All previous generations of LTO cartridges have used a type of pigment called a Metal Particulate (MP). This pigment gets its magnet properties from the needle-like shape of the particle. See Figure 1 for an image of a tape using MP particles under a Scanning Electron Microscope (SEM). For LTO6 there is a second pigment type that is also being used Barium Ferrite (BaFe). BaFe has been around for many years and has been used in other data storage media formats. The magnetic properties of the BaFe particle are derived from its hexagonal crystal structure that looks like a plate. See Figure 2 for an SEM image of a tape using BaFe particles. Figure 1. SEM image of tape using MP particles Figure 2. SEM image of tape using BaFe particles

2 Since MP gets its magnetic properties from the needle-like shape of the particles, this same geometry inherently makes it difficult to reduce the size of the particles beyond the current state. BaFe, on the other hand, derives its magnetic characteristics from the crystal structure of the particles which makes it possible to create smaller magnetic particles. The ability to make smaller particles is the one main advantage of BaFe as it allows more particles-per-unit volume and therefore improves the Signal to Noise ratio as described in the next section. However, due to the nature of the BaFe crystal structure, the BaFe particle has a smaller magnetic moment. This means that the signal from the tape has lower amplitude (by about half) for a BaFe tape compared to an MP tape. Figure 3 shows servo signals from BaFe and MP tapes, note the lower amplitude of the BaFe tape. Higher amplitude from the servo signal will provide more robust tracking (the ability of the head to stay on the data track) in the event of high system noise (defined in the next section). Similarly, higher output is also observed on a data channel with MP based tapes. Figure 3 Servo Signals from MP and BaFe Tape SNR AND OTHER MAGNETIC PROPERTIES One key parameter for any storage medium is the Signal to Noise ratio (SNR). The SNR provides a measure of the data signal relative to noise. There are two main sources of noise media noise and system noise. Media noise is generally inversely proportional to the number of particles within a recorded bit, so increasing the number of tracks or increasing the number of bits stored down the length of a tape will cause the media noise to increase relative to the data signal. Increasing the number of particles will give better SNR due to media noise. The BaFe particle has an advantage in this case as its physical shape allows for more particles per unit volume. System noise is caused by the electronics within the system. Noise in the mechanics, read/write head, amplifiers and motors are sources of system noise. Also, the data being transferred and stored within the circuit board and across the cables connecting a drive to a computer can also be sources of system noise. Increasing the number of particles in the media will not benefit the system noise component of SNR and the higher moment MP media with its higher signal amplitude will therefore have an advantage in this case. ARCHIVABILITY Tape products continue to be the medium of choice for long-term archival storage of data. In many cases, data may need to be stored for up to 30 years. Tape simply provides the best technical and economical solution in this application. There are several ways in which magnetic 2

3 tape can degrade over time. Generally there are three primary factors that contribute to performance decline in tape. These factors include: Moment Loss Spontaneous Erasure Binder integrity Moment loss is due to the magnetic particle losing some of its magnetic properties. The core of an MP particle is sensitive to oxidation so MP particles have a thin outer layer called a passivation layer which is present to protect the particle from oxidizing. However, some oxidation still occurs. The particles will lose magnetic moment over time reducing the signal that can be read from the tape. Studies have shown that the particle will lose <10% of the moment over a 30-year period when stored at room temperature and moderate humidity. Figure 4 shows the results of a study done by Fujifilm (2010). In this study, tapes were stored in a high temperature and humidity environment to accelerate the effects of time where one day is the equivalent of one year in a normal room environment. The data shows good performance by both the MP and the BaFe tapes as a demagnetization rate of <10% has negligible impact on signal integrity Figure 4. Moment loss for MP and BaFe tape showing acceptable performance by both types of particles (1 day on graph = 1 year in use) Spontaneous erasure is the abrupt change in magnetization caused by thermal energy. Resistance to spontaneous erasure is driven by the size of the particle and how large of a magnetic field is required to make a particle switch (called the coercivity). As particle sizes gets smaller and smaller, they have more and more tendency to spontaneously change magnetization. This is referred to as the thermal stability of the particle. Since the BaFe particle is smaller than the MP particle, it has a higher tendency to spontaneously change magnetization. However, it still has an archive life of more than 30 years. Binder integrity is the ability of the binder to not break down over time. The binder is the glue that holds the particles on the film and this technology has come a long way. In many older formats, the binder was the main source of long term tape degradation and the limiting factor in the life of the tape. Currently there is no evidence to suggest that magnetic pigment particle type affects binder integrity. In Drive Performance End users of tape are primarily concerned with in drive performance because backup time, tape capacity and data integrity are determined by the interaction between the tape cartridge and the drive. There are many factors that can contribute to drive performance which also rely on the quality and configuration of MP or BaFe magnetic particles. Drive performance can be measured by: Magnetic performance SNR and Signal Amplitude Run ability 3

4 Durability Head wear The SNR and signal amplitude of tape can affect the performance of a drive if the levels drop below a certain threshold. However, the LTO technology consortium has developed very tight specifications for SNR and amplitude and both MP and BaFe meet these requirements. However for overall signal integrity, BaFe tapes offer advantages in SNR while the MP tapes have advantages in higher amplitudes for both the data signal and the servo signal due to the physical nature of the particles as discussed earlier. Run ability of tape within a drive can be affected by tape roughness and debris generation over time. Debris generation is often governed by the binder (glue) formulation used by the tape manufacturer. Pigment type itself has not been shown to be a significant contributor to debris generation. Tape roughness is engineered for a specific product. Each generation of tape for LTO has tended to be designed smoother than the generation before in order to get more intimate head-to-tape contact. Smoother tape, however, does have the adverse effects of higher tape path friction especially at turnarounds when the tape has to change direction. These factors have all been taken into consideration in the tape and drive designs. Simply put, the drive manufacturers have designed their drives to work well with both the MP and BaFe based tapes. Each manufacturer is also responsible for setting its durability requirements. Imation LTO6 cartridges are tested to withstand 200 full file writes (about 35 days of continuous 24 hour use) with no significant change in error rate. Figure 5 shows the change in the error rate for each data channel during a typical 35 day test. Error rates remained relatively unchanged during the duration of the test. Figure 5. Example of a 35 day test for an Imation LTO6 cartridge showing very little change in error rate The life of a drive is typically determined by the read/write head in the drive. The media run on a head will also affect the life of the head. Generally, the formulation of the tape determines the wear characteristics and not the type of magnetic pigment used. LTO drive manufacturers require all tape manufacturers to pass tests to determine the amount of wear on a head by a given tape formulation. This test is referred to as a Green Tape Test because many new (Green) cartridges are tested in a drive to determine the effect of the tape on the head. All LTO licensed tape manufacturers products, whether MP or BaFe designed tapes, have passed these tests. Figures 6 and 7 are results that Hewlett Packard (2013) has published in a recent study showing no change in capacity during such a green tape test. 4

5 Figure 6. MP Green Tape Test (from HP) Figure 7. BaFe Green Tape Test (from HP) CONCLUSION An advantage of BaFe tape is that it offers improvements in SNR due to the relative media noise level. It is likely that a smaller pigment tape like BaFe will be preferred over MP for future tape generations since smaller particles will be required to achieve larger cartridge capacities. However, for LTO6 the additional SNR does not improve the uncorrected error rate and it does not improve the 30 year archival life of the cartridge. MP tape has a proven track record of performance reliability with five generations of tape use. Businesses may also want to consider previous tape generation track records. LTO6 tape drives are designed to work with all the LTO6 licensed tape manufacturers LTO6 media whether they are MP or BaFe pigment type tape. They are also required to be backward write- and read-compatible with LTO5 tape and backward read-compatible with all LTO4 tape. Both generations of LTO5 and LTO4 tape are MP based. In summary, future formats may require BaFe style pigments, but for LTO6 both tape types meet all the stringent LTO6 requirements set forth by the LTO technology consortium and will perform well for end user applications. REFERENCES FujiFilm. (September 10, 2010). Long-term Archivability and Stability of Fujifilm Magnetic Tape Using Barrium Ferrite (BaFe) Particle. Retrieved from Hewlett Packard. (January 10, 2013). Best of Both Worlds. HP LTO-6 Media Metal Particle and Barium Ferrite. [PDF]. Retrieved from 5