IBM System Storage TS3500, Введение и руководство по планированию

Страница: 201 / 290

about implementing segmentation and capacity scaling, refer to the README files
that pertain to your device driver on the web:
http://www.ibm.com/support/fixcentral
For more technical information regarding WORM, capacity scaling, and
segmentation, see also the
IBM System Storage 3592 Tape Drive SCSI Reference .
All TS1120 and later tape drives also support multiple format options, such as
scaling and segmentation modes, to allow you to trade capacity for improved
access times. While 256 settings of the Capacity Scaling byte (and resulting
fractional capacities) are supported on these drives, the following three primary
settings are recommended for use:
v
Full capacity default mode
v
20% scaled fast access mode (20% capacity scaled, front of tape used). The
Capacity Scaling byte is x'35'.
v
Performance scaling for 87% capacity and a segmented format with recursive
accumulating backhitchless flush (RABF) capability (a non-volatile caching
technique) for the full cartridge. For WORM firmware for the 3592 tape drives,
the Capacity Scaling byte is x'E0'.
These settings are fully certified and are available as labeled and initialized
part-numbered cartridges. For the exact Mode Select commands and settings that
are necessary to invoke scaling, see the
IBM System Storage 3592 Tape Drive SCSI
Reference .
Scaling support in drive
Capacity scaling in the TS1120 and later tape drives is controlled by the host
program performing a Scaling operation. This is performed using the Capacity
Scaling byte and the Capacity Scaling Valid control bit in Mode page X'23'. These
tape drives do not change current cartridge scaling unless a SCSI Mode Select
command that specifies Mode Page X'23' (with appropriate non-default parameter
settings) is received while the cartridge is positioned at the beginning of the tape.
The drive can sense and report the scaling state of the current medium by using a
Mode Sense command that specifies Mode Page X'23'. The default unscaled
capacity is 300 GB (279.39 GiB) for a JA cartridge in J1A density, 500 GB (465.66
GiB) for a JA cartridge in E05 density, 700 GB (651.93 GiB) for a JB cartridge in E05
density, and 1 000 GB (931.32 GiB) for a JB cartridge in E06 density. The default
unscaled capacity is for a JY cartridge in E07 density is 4 TB (3.64 TiB).
v
The cartridge can be rescaled from any current Capacity Scaling byte value to
any supported new value. The tape is logically erased by this (End of Data mark
written at beginning of tape), but not physically erased as with the long erase
command. Scaling or rescaling one cartridge does not cause rescaling of the next
cartridge; an explicit command must be issued for each cartridge to be rescaled.
v The drive provides the option of setting the scaling values of N/256ths of full
capacity, where N ranges from X'16' (22 -- equals about 8% capacity) to X'EC'
(236 -- equals about 92%)
v
For scaling factors N, between X'4B' and X'EB , the drive scales to the specified
amount and creates a fast-access 20% capacity segment in the beginning of the
scaled region.
v
At all scaling factors, the drive supports early warning at the end of the scaled
region (with the appropriate unit attention to inform the software that it should
flush buffers and close volume) and reports a physical end-of-tape check
Chapter 5. Using 3592 tape drive media
177