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Drive Speed and Capacity Comparisons

The table below summarises the capacity and throughput of some tape drives. Click on the link to see more detail for a given drive. Capacity figures are native, that is, uncompressed. Mainframe tapes will generally hold three times as much data with compression, and Open Systems data two times as much. Throughput figures are for sustained speed without compression, and assumes that all connectivity can be driven that fast. Throughput Density is the ratio of tape capacity to transfer speed, and is an indication of the tape drive's performance. The lower the figure, the better the performance. However, it does not tell the whole story. A tape drive which supports fast positioning can have a high throughput density, but can still perform well.
I'm quoting drive speeds in Gigabytes per hour, rather than the more traditional Megabytes per second. This is because tapes are usually used for backups and we measure backup requirements in Gigabytes. It seems to me that a gigabytes per hour measure is more useful.

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Drive type Format Max Native Capacity Sustained transfer Speed Throughput Density
LTO-7 Linear 6 TB 1,052 GB/hour 5.7
TS1150 Linear 10 TB 1,265GB/hour 7.9
T10000D Linear 8TB 900GB/hour 8.8

   

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Drive details

LTO

Linear Tape Open (LTO) has pretty much won the Open Systems tape war, having seen off rivals DLT and AIT and now accounting for more than 96% of tape drives sold.
LTO gets its high capacity by writing up and down the tape several times, the LTO format will record up to 3584 tracks across a 1/2 inch tape. It can write in either direction, so it writes tracks down the tape, reverses, and writes back up again. It also has embedded 'servo tracks' to allow fast location of specific data on a tape. Also, LTO has few moving parts. This makes the product reliable and easy to maintain. LTO now supports WORM media for compliance purposes.

LTO5 and upwards provides the tape partitioning support that LTFS requires. LTFS (Linear Tape File System) allows you to mount a tape drive the same as a disk and view the contents of a tape in the same way that you can look at a disk. This means you don't need special backup and recovery software to access the tape data, you can just use drag and drop to copy the data.

LTO uses a single-reel, and is typically used for very high capacity backup. LTO-7 capacities and speeds are :-

  • data access in under 10 seconds,
  • capacities of up to 6 Terabytes native
  • transfer rates 1 TB/hour uncompressed

LTO7 high capacity is achieved by using 3584 data tracks over the half inch tape, compared with 2176 tracks for LTO6. These tracks are split into 4 bands and data is written to the innermost band first, to provide protection to the data recorded earliest in the process. LTO7 has 32 tape heeads, so on the first pass of a round trip down the length of the tape, the first set of 32 tracks are read, or written, concurrently. At the end of the tape, pass two of the round trip starts. The read/write heads are indexed and positioned over next set of tracks, and the tape reverses direction back toward the beginning of the tape to complete the round trip. Data is written 14 times in each direction per band, or 28 times in total per band, so the total tracks is 4 * 28 * 32 = 3584.

LTO-8 may arrive at the end of 2017 and is planned to deliver 12.8TB raw capacity and 32TB compressed, with 472MB/sec native and 1.18GB/sec compressed transfer rates.

When the LTO standard was originally developed, it was envisaged that there would be two types of LTO, Ultrium; large capacity and slower and Accelis; small capacity but fast. The Accelis format was designed for applications that require exceptionally fast access times, such as online data inquiry and retrieval. No products were ever produced as there was no market for them. The Ultrium name has now been dropped and the technology is usually just called LTO.

The Linear Tape section explains the LTO technology in detail

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TS1150

The IBM TS1150 is a progression of the old mainframe Magstar technology. The original Magstar was called 3590. The 3592 drive was a complete change in track format, and is not compatible with earlier 3590 Magstar models. The models have since progressed from TS1120 to TS1150. The following table compares the TS11x0 models. All these drives support WORM media for Sarbanes-Oxley compliance. The TS1130 supports 4Gb Fibre Channel and 4Gb FICON, as well as standard ESCON.

  TS1150 TS1140 TS1130 TS1120
Native Capacity 10TB 4TB 1TB 700GB
Native sustained transfer speed 1,265GB/h 878GB/h 560GB/h 360GB/h
Buffer size 2GB 1GB 256MB 128MB

The TS1150 capacity depends on the tape media type and varies between 10TB with JD/JZ media, 7TB with JC/JY media and 2 TB with JL media.
The TS1150 has 12 read/write speeds to enable the drive to stream data from slower hosts, improving throughput and reliability;
The TS1150 2GB buffer allows it to read ahead and cache more data for better performance in “short hop” file locate operations
The backwards compatibility feature enables the TS1150 to read/write to a TS1140 cartridge and reformat that cartridge to a 7TB capacity
LTFS allows users to organize and search tape media with the same access methodology as a hard disk, thus simplifying the storage and retrieval of files on tape

The TS1150 will support a burst data transfer rate of 800MB/s per second with FICON connectivity, and the native capacity can be reduced to 500GB for sets of small files which need a high retrieve performance. It uses a bi-directional longitudinal serpentine recording technique, writing to 2560 tracks (The TS1130 uses 512 tracks). The TS11x0 drives are smaller than the older 3590, and so its possible to replace a 3590 drive in a 3494 tape library with two TS1140 drives. These are native speeds and capacities. IBM quote 2:1 compression for open systems and 3:1 for mainframe data, which in practical terms will increase capacity and throughout.

The TS11x0 eliminates some tape back-hitching. Most tape drives store data in a buffer which is then flushed out to tape when the application completes sending a block of data. The tape drive overruns then back-hitches to the correct point on the tape, ready to write the next block of data. The TS11x0 will write this block of data to a temporary space on the tape, and retain the data in the buffer. It can then write out several data blocks when the buffer is nearly full. This reduces tape wear, as well as improving performance.

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StorageTek T10000D

Oracle, through SUN, has inherited the StorageTek range of tape drives. They are still called StorageTek tapes on the Oracle site (February 2017), so I'll continue to use the StorageTek name. StorageTek drives are all a proprietary format, which basically means that you have to source your cartridges from StorageTek.

StorageTek's flagship drive is the T10000D, which uses a 32 channel linear architecture. It was released in 2013 and has a 2GB buffer and supports encryption, WORM, 16Gb Fibre Channel and FICON and emulates an IBM 3592. It can hold 8TB native. 'Sport' cartridges are available that hold less capacity, but have a much lower throughput density.

The StorageTek tape feeds and speeds are summarised below.

Drive Type Native Capacity Native transfer speed Throughput Density WORM support Encryption Support
T10000D 8.5TB 885 GB/h 9.6 YES YES
T10000C 5TB 885GB/h 5.64 YES YES

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Minor and Obsolete Tape Technologies

DAT

DAT stands for Digital Audio Tape and was originally intended for audio recording. Sony and HP orignially defined the DDS (Digital Data Storage) standard for computer data storage. Sony stopped developing DAT technology in 2005, but it is still manufactured by HP and Quantum.
DAT technology is based on helical scan, and uses 4mm tapes, similar in size to an audio cassette cartridge.

DAT reliability has improved over the years, MTBF is now quoted at 300,000 hours or 34 years. Other sources quote DAT can be used for 2,000 reads or 100 writes before the cartridge should be replaced. Modern HP StorageWorks DAT drives are now available with capacities up to 72 GB and SCSI, USB 2.0 and SAS interfaces
DAT comes in different formats and lengths as shown in the table below

Drive Type Raw Capacity in GB Transfer speed in MB/s Media length (m) Media Width (mm) Connectivity
DAT73 36 3.2 170 3.81 SCSI/USB
DAT160 80 6.9 150 8 SCSI/USB/SAS
DAT320 160 86 GB/h 150 8 USB2/SAS

Capacity quoted above is all uncompressed. You will at least double capacity if your DAT drive supports compression, but you will not be able to read it back on a drive which does not support compression. Also, some operating systems do not support the SCSI commands to switch compression on/off. Drives generally compress by default.

If you want to ensure your DAT tapes are always compatible then consider the following

  • Drives which support compression should be hardware switched with compression off, and not software switchable.
  • Don't use 120m tapes
  • use the 'noswap' device on IRIX when moving data to a non-IRIX system
  • use a 128 blocking factor on IRIX when moving data to a non-IRIX system ... when reading a 'foreign' DAT use 'mt blksize' to determine the blocksize and use that figure in the tar command.

The DAT320 supports encryption

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Tandberg / Exabyte

Exabyte was originally founded by a group of former STK employees, but they were bought out by Tandberg and the name Exabyte has just about disappeared.
Tandberg in turn had its own SLR140 range, wih a capacity of to 140 GB and transfer rates of up to 43.2 GB/Hr, but it now sells LTO drives.

DLT-S4

Quantum owned the DLT technology and licensed it out to lots of companies, including Compaq, IBM, Hewlett-Packard, Dell, and SUN. DTL tape drives were discontinued in 2007, though there are doubtless lots of old drives out there. Quantum now make LTO and DAT drives.

AIT

Sony withdrew Advanced Intelligence Tape from the market in March 2010. The top range product offered a capacity of 400GB with a data transfer rate of 108 GB/hour. It had a 72Mb 'Memory in Cassette' (MIC) which could store index information for faster access.

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