Tandberg SLR: a superior alternative to DDS. (DDS Replacement).
There are two main technologies of tape drives for backup: Helican Scan and Linear Recording.
Helical Scan Products: Track is recorded diagonally in "stripes" across face of longitudinal tape. All current helical scan products utilize a dual hub driven cassette/cartridge and a rotating multi-channel recording head. A separate motor is required to control each tape hub as well as one for spinning the recording head (three electric motors).
In addition the tape guidance path on all helical drives is contained fully inside the drive (requiring precision mechanical components/guides) adding complexity/cost. Generally two other actuator motors are required for cartridge housing load/unload and tape threading/wrap around the head.
As far as capacity futures are concerned DAT/DDS, 8mm, AIT, and VXA helical scan products have less available total tape area than the linear technology products Travan, SC50, SLR, LTO, and DLT tape formats. While the smaller cartridge size is "sexy" it is a liability when it comes to ultimate data storage capacity.
Linear Recording Products: Tracks are recorded parallel with face of longtitudial tape. In linear drives the basic recording technique is similar between Travan, SLR, SC50, VS, DLT, and LTO drives (there are variations in recording density/encoding, track pitch, and number of parallel channels). However there are differences in how the tape is handled between the single reel cartridge based drives and the dual reel cartridge based drives.
The larger recording surface provided by linear technology drives allows for greater storage capacities in linear products at equivalent data packing densities. Linear recording technique also allows the scaling of data transfer rate, adding more recording channels in parallel. In contrast, It is more difficult to substantially increase the transfer rate on helical formats by addition of parallel channels. Limitations come in to play related to relative head to tape speed with helical scan drives where both the tape and the head are moving.
Within the linear recording technology, SLR tape drives utilize cartridges that contain both tape guidance components and a portion of the tape drive system. This makes for a more complex cartridge, but the benefit is the tape drive mechanics required to make use of the cartridge are simplified. SLR tape drives only require one motor to drive the tape, one to two actuators to move the head, and one motor to load/unload the tape. An added benefit of this system is less probability of having interchange problems between different drives. In other drive styles, which fully contain the guidance mechanics in the drive, it is possible to have minor variations in track placement between drives (leading to data interchange problems).
All DLT and LTO style drives require a take up reel located in the drive, so these drives require two drive motors for tape motion. In addition the tape cartridge contains no tape guidance facility thus the drive must contain the precision tape path. These characteristics result in additional cost and also means the tape/drive system is more susceptible to the interchange errors mentioned previously.
Cost of Ownership
Mainstream hard disk drive capacity is moving from 18GB to 36GB and soon to 73GB. Tape backup and restore must grow with these capacities. The need to have all backup data on a single tape cartridge, particularly during a restore process. is critical to increased security and easier administration. Smaller backup windows necessitate faster transfer rates as well. The capacity requirements and the backup/restore times will be important factors to consider in the total cost of ownership.
Price at the time of purchase is often a critical factor. However if one looks at cost of ownership over time (e.g. three years) the picture may change both for the customer and the seller. For a backup system one has to take into account the reliability of the tape drive, and reliability and durability of the media. Annual failure rate (AFR) tells something about how many tape drives of a population may have to go to service per year, and also what the chance is for failure during backup and/or restore. There are also big differences in durability of the media cartridge between the different technologies. Exchanging the tape cartridge every year vs. changing cartridges only every third year has a big impact on overall cost of ownership. The durability of the tape cartridge is not only caused by number of passes of the media over the head, but also by the ruggedness of the cartridge itself.
Where the cost and reliability differences between the technologies come into play are in the components used directly for the recording process such as the magnetic heads, electric motors required, actuators required, and precision mechanical components to implement the recording format. In these areas the technologies vary widely. Less parts typically mean higher reliability. The head design is a big contributor to reliability. Reliability also has to do with how well the microcode (or firmware) for controlling the hardware and host interface is tested and proven.
Tandberg Data--A Generation of Experience
Tandberg Data has over 50 years of experience in reading and writing on magnetic tape media, and the company has been a pioneer in computer data cartridge formats for the last 20 years. Over 3 million tape drives based on SLR technology have been manufactured.
The SLR family uses advanced technologies including VR2 encoding for additional data density, dynamic servo tracking for additional reliability, shock resistance, and capacity, and an engineering methodology where data formats on tape are created to provide maximum capacity/performance with minimum interchange "baggage."
How can SLR technology be the technology of choice in the SMB market segment?
Product Family: The SLR product family starts at 1.2GB/3Mbs and already has two products available beyond the 20GB (DDS) product category and offers native 50GB/5Mbs drives today.
SLR drives have cost effective autoloader and library technology up to 4TB available today as well.
Reliability: The current SLR products dynamically adjust recording parameters and have tracking servo to insure maximum reliability, interchange capability and long service life without problems. With its few moving parts, rugged tape cartridge that is very durable, a well designed read/write head and well proven firmware, the SLR product family is regarded by customers as the most reliable tape drive offered in the SMB segment. The quality and reliability has been demonstrated also in dusty environments and when used by untrained personnel like in POS environments and doctors offices.
The SLR tape drives have advanced diagnostics and continually demonstrate less than 1.5% annual field failure rate. A critical factor in determining how well your tape drive will perform when you really need it.
Price Point: SLR technology, which requires fewer motors and less precision mechanical parts content than helical scan products or DLT type drives, is positioned well for aggressive market pricing. The SLR3 (1.2GB/ .3MBs) through SLR5 (4/8GB.38/ .76MBs) are positioned in the low/entry level server and workstation segment. SLR7 (20/40GB and 3/6MB), SLR60 (30/60GB and 4/8MB), and SLR100 (50/100GB and 5/l0MB) are positioned in the entry level server and the higher end workstation segments. The 20/40GB SLR7, with the same or better performance that the DDS4 products, is price positioned well below the DDS product.
Performance: SLR technology has short media load/unload times, supports partitioning of media for QFA directories required by some software packages (just like DDS), and all SLR cartridge formats have special features for improving block seek times. In addition higher capacity drives support automatically adjusted multiple transfer rates optimizing throughput. The advanced VR2 encoding means greater storage capacity and higher transfer rates with less data channels. The in-line data compression technology used on SLR7 and higher-capacity SLR drives gives a unique performance for data compression vs. the look-aside technology used by most of the others. Tests have shown a transfer rate of over 30MBs on SLR 100 with highly compressible data.
Backwards compatibility and scalability: Tandberg Data has committed to backwards compatibility on the SLR tape drive. In many cases, customers can use older tape media on higher capacity tape drives. This guarantees that customers can grow with this technology as capacity and performance needs increase.
Support: SLR technology has broad software support, All technical documents and current firmware images are downloadable from our website. Tandberg Data offers toll free technical support as well. Tandberg Data has implemented advanced management information features that allow the user to know the "health" of their drives as well as the media they use with it.
SLR technology provides the reliable, high-performance, high-capacity tape drives you need to secure your data today and well into the future. In a market crowded with choices customers will be looking for solutions that can be used today and promise a cost-effective future.
Willy A. Johansen is corporate SLR product manager at Tandberg Data ASA
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|Author:||Johansen, Willy A.|
|Publication:||Computer Technology Review|
|Date:||Aug 1, 2002|
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