HP Q153090901 - Manual (Page 21)

CD-ROM emulation
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Although there are no actual Field Replaceable Units on HP Ultrium drives, the following sub-
assemblies can be replaced at Repair Centres:
CD-ROM emulation
The One Button Disaster Recovery (OBDR) functionality in HP Ultrium drives enables them to
emulate CD-ROM devices in specific circumstances (also known as being in “Disaster Recovery”
mode). The drive can then act as a boot device for PCs that support booting off CD-ROM.
A CD-ROM capable drive can be switched into CD-ROM mode by powering on with the eject
button held down. The drive then alters its behavior as follows:
• The front panel lights flash a “warbling” sequence.
• CD-ROM commands are executed (as opposed to tape drive mode when they would be
rejected). Commands specific to CD-ROM mode are READ 10 , READ TOC and READ
CAPACITY . In the case of SCSI commands 08h ( READ ), 1Bh ( LOAD/UNLOAD ) and 2Bh
( LOCATE ), these are interpreted as CD-ROM commands 08h ( READ 6 ), 1Bh ( START/STOP )
and 2Bh ( SEEK ) respectively.
• Writing is disabled.
• Normal INQUIRY data is modified to add a field indicating that the drive supports CD
emulation and to switch the peripheral device type field to indicate a CD-ROM drive.
• The mode header and mode block descriptor are modified.
• A CD-Emulation mode page is added.
• Mode data changes to reflect CD-ROM medium type and block size.
• Status reporting by the media access check is altered.
• The drive’s sense data when the media is not ready for access always indicates “loading”.
If a tape is inserted while the drive is in CD-ROM mode, the drive assumes that it will contain an
image of a CD offset 20 blocks into the tape. It reads the first 250 kilobytes of this image into
buffer space reserved for CD-caching. It then looks for a special message (“
EL TORITO
SPECIFICATION
”) at the 8th byte of the 18th record of the image. If the drive fails to find this
message, it ejects the tape and waits in CD-ROM mode for a properly-written CD-image tape to
be inserted.
The drive will remain in CD-emulation mode until one of the following occurs:
• A MODE SELECT command switches it back to tape drive mode using the CD-emulation
mode page.
• Drive PCA • Head Assembly
• Mechanism • Front Panel