HP LTO 4 FC, LTO 4 SCSI, LTO 4 SAS Designing software to use the TapeAlert log, TapeAlert models

NOTE: Once cleared, a flag cannot be set again until the specified clearing conditions are met. So, for example, if the cartridge in the drive is not of data grade, once flag 8 has been cleared, it cannot be set again until the cartridge has been removed.

Designing software to use the TapeAlert log

When writing software to take advantage of the ability of a drive to predict problems and actions that a user should take, it is important not to exclude drives that do not support this feature. For this reason, the application should first check whether the TapeAlert Log page is supported by the drive and then use one of two methods to access the information:

•Use the MODE SELECT Informational Exceptions mode page to enable “Check Condition” mode. This means that the tape drive reports CHECK CONDITION on the next SCSI command after one or more TapeAlert flags are set. When CHECK CONDITION is received, the host software should behave as follows:

a.It issues a REQUEST SENSE command. Additional sense of 5D00h indicates that the CHECK CONDITION was caused by TapeAlert. This enables the software to distinguish CHECK CONDITIONs caused by actual errors and those resulting from a TapeAlert flag being set.

b.The software reads the TapeAlert log page to discover which flags are set (even for CHECK CONDITIONs caused by actual errors).

Note that when CHECK CONDITION results from TapeAlert, the command that reported the CHECK CONDITION is not in error and will have completed successfully. It follows that the software should not repeat the command.

•Read the TapeAlert log page using LOG SENSE at the following times:

•Immediately after a SCSI CHECK CONDITION/REQUEST SENSE cycle.

•At the end of each tape where a backup or restore spans multiple tapes. The host must read the TapeAlert log page before a tape is ejected.

•At the end of a backup or restore.

It is also advisable to poll the TapeAlert log page every 60 seconds while the tape drive is idle.

Using “Check Condition” mode is recommended over polling because it guarantees that the software will be aware of any TapeAlert flag being set. It is theoretically possible that TapeAlert information could be missed when polling, though the higher the frequency of polling, the smaller the chance is.

TapeAlert models

SSC-3rev02 specifies three optional methods for an application to monitor activation of TapeAlert flags. LTO 4 drives support two of those models:

•Polling the TapeAlert log page (2Eh) or the TapeAlert Response log page (12h);

•Configuring the device server to establish an Informational Exception condition (via mode page 1Ch) upon activation of one or more TapeAlert flags.

These are described in more detail below.

HP LTO Ultrium 4 drives technical reference manual, volume 2: software integration 87 HP restricted