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- Helical Scan
- Tape drive comparisons
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- Tape Error Handling
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.
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.
|Drive type||Format||Max Native Capacity||Sustained transfer Speed|
|LTO-8||Linear||12 TB||1,215 GB/hour|
|TS1160||Linear||20 TB||1,400 GB/hour|
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 :-
LTO7 and 8 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. LTO8 has 32 tape heads, 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 is backward and forward compatible with LTO7, and supports 256 byte AES encryption.
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
The next two tape drives are mainly used in Mainframe environments.
The IBM TS1160 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.
|Native sustained transfer speed||1,400GB/h||1,265GB/h||1,265GB/h|
The TS1160 Tape Drive, an upgrade from the TS1155, supports JE and JD media formats in both read and write mode, and can fill both format tapes to 20TB native, a 25% increase over the TS1150. The TS1160 also offers built-in data encryption capabilities and supports a native data transfer rate of up to 400 MBps. It also supports IBM Spectrum Archive. The 2 GB internal data buffer offers improves read performance for random skip forward sequential activities typically seen on database searches.
The drive comes with either FC-16 Gb or Ethernet 10Gb interface attachment for connection to a SAN, or to Hyperscale and RHEL environments with an Ethernet 10Gb interface.
Offboard data string searching enables data content searching of host records for string matches offboard from the host server. The tape drives can perform this search at maximum data rate (400 MBps native) while it would take much longer for a host server to read the data, buffer the data to disk, and then parse the actual data stream with host software routines. The TS1160 supports IBM Spectrum Archive which uses LTFS which allows direct access to data stored on a tape direct, intuitive and graphical access to data stored in IBM tape drives and libraries by incorporating the IBM Linear Tape File System™ (LTFS) format standard. LTFS compatibility allows tape-stored data to be accessed as if it were on disk or flash storage.
The TS1160 supports 3592 WORM cartridges and media partitioning for more flexible data management. As stated above, the TS1160 can use both JE and JD cartridges, but media written in TS1160 format cannot be read by TS1155 or TS1150 drives. TS1160 can also write to JE media and JD media in both TS1155 format with a 15 TB capacity, and TS1150 format with a 10 TB capacity. It can read and write to JC media in TS1150 format with a 7 TB capacity, and read 4 TB JC media in TS1140 format.
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|
Oracle StorageTek did plan to release a T10000E drive in 2017 with a capacity of up to 16 TB, but development was cancelled in 2016. The T10000D is still supplied for use in some of the StorageTek robotic tape libraries, but it seems that Oracle will concentrate on LTO-8 tape drives in future.
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|
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
The DAT320 supports encryption
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.
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.
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.