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| author | Dave Kleikamp <shaggy@austin.ibm.com> | 2006-01-24 14:34:47 -0600 |
|---|---|---|
| committer | Dave Kleikamp <shaggy@austin.ibm.com> | 2006-01-24 14:34:47 -0600 |
| commit | 0a0fc0ddbe732779366ab6b1b879f62195e65967 (patch) | |
| tree | 7b42490a676cf39ae0691b6859ecf7fd410f229b /Documentation/cciss.txt | |
| parent | 4d5dbd0945d9e0833dd7964a3d6ee33157f7cc7a (diff) | |
| parent | 3ee68c4af3fd7228c1be63254b9f884614f9ebb2 (diff) | |
Merge with /home/shaggy/git/linus-clean/
Diffstat (limited to 'Documentation/cciss.txt')
| -rw-r--r-- | Documentation/cciss.txt | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/Documentation/cciss.txt b/Documentation/cciss.txt index 68a711fb82c..15378422fc4 100644 --- a/Documentation/cciss.txt +++ b/Documentation/cciss.txt @@ -133,3 +133,32 @@ hardware and it is important to prevent the kernel from attempting to directly access these devices too, as if the array controller were merely a SCSI controller in the same way that we are allowing it to access SCSI tape drives. +SCSI error handling for tape drives and medium changers +------------------------------------------------------- + +The linux SCSI mid layer provides an error handling protocol which +kicks into gear whenever a SCSI command fails to complete within a +certain amount of time (which can vary depending on the command). +The cciss driver participates in this protocol to some extent. The +normal protocol is a four step process. First the device is told +to abort the command. If that doesn't work, the device is reset. +If that doesn't work, the SCSI bus is reset. If that doesn't work +the host bus adapter is reset. Because the cciss driver is a block +driver as well as a SCSI driver and only the tape drives and medium +changers are presented to the SCSI mid layer, and unlike more +straightforward SCSI drivers, disk i/o continues through the block +side during the SCSI error recovery process, the cciss driver only +implements the first two of these actions, aborting the command, and +resetting the device. Additionally, most tape drives will not oblige +in aborting commands, and sometimes it appears they will not even +obey a reset coommand, though in most circumstances they will. In +the case that the command cannot be aborted and the device cannot be +reset, the device will be set offline. + +In the event the error handling code is triggered and a tape drive is +successfully reset or the tardy command is successfully aborted, the +tape drive may still not allow i/o to continue until some command +is issued which positions the tape to a known position. Typically you +must rewind the tape (by issuing "mt -f /dev/st0 rewind" for example) +before i/o can proceed again to a tape drive which was reset. + |