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Cartridge compatibility
The LTO-2 uses the IBM LTO Ultrium 200 GB Data Cartridge and is compatible
with the cartridges of its predecessor, the IBM Ultrium Internal Tape Drive (called
Generation 1). The LTO-2 performs the following functions:
v Reads and writes Generation 2 cartridges to Generation 2 format
v Reads and writes Generation 1 cartridges to Generation 1 format
v Does not write Generation 2 cartridges to Generation 1 format
v Does not write Generation 1 cartridges to Generation 2 format
The LTO-2 reads tapes that have been written by other licensed Ultrium 2 drives. It
also writes to tapes that can be read by other licensed Ultrium 2 drives.
In addition to using the IBM LTO-2 Ultrium Data Cartridge with up to 200 GB
capacity, the LTO-2 also offers read/write capability for certified LTO Ultrium tape
cartridges.
Speed matching and channel calibration
To improve system performance, the LTO-2 uses a technique called speed matching
to dynamically adjust its native (uncompressed) data rate to the slower data rate of
a server. With speed matching, the drive operates at one of five speeds when
reading or writing the Generation 2 cartridge format to achieve a native data rate
of 17.5, 21.9, 26.25, 30.63, or 35 MB per second (MB/s). If the server's net
(compressed) data rate is between two of the preceding native data rates, the drive
calculates which of the two data rates at which to operate. (For example, if the
server transfers data at 60 MB/s on the host bus, at 2:1 compression its net data
rate is 30 MB/s. The drive will then dynamically choose to operate at a native data
rate of 26.25 or 30.63 MB/s, whichever enables it to successfully receive the
greatest amount of compressed data over the network.) Speed matching
dramatically reduces backhitch, the condition that occurs when a tape stops,
reverses, and restarts motion. A backhitch is usually the result of a mismatch
between the data rates of the server and the drive.
System performance is further optimized by a feature called channel calibration, in
which the drive automatically customizes each read/write data channel to
compensate for variations in such things as the recording channel's transfer
function, the media, and characteristics of the drive head.
Sleep mode
To conserve energy when circuit functions are not needed for drive operation, the
LTO-2 features a power-management function that causes the drive's electronics to
enter a low-power mode known as sleep mode. To enter sleep mode, the drive must
be inactive for a minimum of 15 minutes; to exit, the drive must receive a
command across the SCSI interface or a load or unload request. When in sleep
mode, the drive's response time to commands that do not require media motion
increases by up to 10 microseconds. Commands that require media motion may be
delayed an additional 100 milliseconds because the tape must be retensioned.
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IBM 200/400GB LTO-2 Tape Drive: User's Guide
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