Dell PowerVault Linear Tape Open (LTO) Basic Knowledge

Answers

1. LTO Media Color Schemes
2. LTO Compression
3. LTO WORM Media
4. Cartridge memory chip
5. WORm Media
   

知识要点：

Ø  戴尔所有LTO磁带外壳（非包装盒）都有明确的颜色可以区分；

Ø  数据带2:1的压缩比率是近似/平均值，实际压缩比率与数据源有关；

Ø  所有磁带中均内置无线存储芯片，所有磁带驱动器均配置有无线存储读写器；

Ø  WORM Media“Write Once, Read Many”的属性针对磁带中的介质段，而非整个磁带；

附：

戴尔官方所提供技术参数

中文：https://china.dell.com/cn/business/p/dell-ultrium-lto-media/pd

英文：https://www.dell.com/us/business/p/dell-ultrium-lto-media/pd

戴尔官方LTO技术手册：https://support.dell.com/support/edocs/stor-sys/LTOmedia/

LTO规范官方地址：www.lto.org

The LTO specification describes a Data Compression method LTO-DC, also called Streaming Lossless Data Compression (SLDC).  It is very similar to the algorithm ALDC  which is a variation of LZS (a patent-encumbered algorithm controlled by Hi/Fn).

The primary difference between ALDC and SLDC is that SLDC does not apply the compression algorithm to uncompressible data (i.e. data that is already compressed or sufficiently random to defeat the compression algorithm). Every block of data written to tape has a header bit indicating whether the block is compressed or raw. For each block of data that the algorithm works on, it saves a copy of the raw data. After applying the compression function to the data, the algorithm compares the "compressed" data block to the raw data block in memory and writes the smaller of the two to tape. Because of the pigeonhole principle, every lossless data compression algorithm will end up increasing the size of some inputs. The extra bit used by SLDC to differentiate between raw and compressed blocks effectively places an upper bound on this data expansion.

LTO-DC achieves an approximately 2:1 compression ratio when applied to the Calgary Corpus. This is inferior to slower algorithms such as gzip, but similar to lzop and the high speed algorithms built into other tape drives. It should be noted that plain text, raw images, and database files (TXT, ASCII, BMP, DBF, etc.) typically compress much better than other types of data stored on computer systems. In contrast, encrypted data and pre-compressed data (PGP, ZIP, JPEG, MPEG, MP3, etc.) would normally increase in size, if data compression was applied. In some cases this data expansion could be as much as 15%. With the SLDC algorithm, this significant expansion is avoided.

WORM media stands for Write Once, Read Many. This means once data is written to a piece of WORM media, the data on the tape cannot be changed or overwritten. WORM media can be appended to if data is already present on the tape. The media also stores unique identifiers which allow the drive to determine whether or not the media has been tampered with. WORM media offers a method of data retention for compliance laws such as the Sarbanes-Oxley Act of 2002. Specific WORM media barcode labels end in LT.

Every LTO cartridge has a cartridge memory chip inside it. It is made up of 256 (128 on LTO-1, 2 and 3) blocks of memory, where each block is 32 bytes for a total of 8 KB (4 KB on LTO-1, 2 and 3). This memory can be read or written, one block at a time, via a non-contacting passive RF interface. This memory is used to identify tapes, to help drives discriminate between different generations of the technology, and to store tape-use information.

Every LTO drive has a cartridge memory reader in it. The non-contact interface has a range of 20 mm. External readers are available, both built into tape libraries and PC based. One such reader, Veritape, connects by USB to a PC and integrates with analytical software to evaluate the quality of tapes. This device is also rebranded as the Spectra MLM Reader and the Maxell LTO Cartridge Memory Analyzer.

WORM media stands for Write Once, Read Many. This means once data is written to a piece of WORM media, the data on the tape cannot be changed or overwritten. WORM media can be appended to if data is already present on the tape. The media also tores unique identifiers which allow the drive to determine whether or not the media has been tampered with.

WORM media offers a method of data retention for compliance laws such as the Sarbanes-Oxley Act of 2002. Specific WORM media barcode labels end in LT.

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