On 7/20/2014 4:54 PM, joystick wrote: > So what happens when the disk tries to write it to the platter and > discovers that there is a media error on that sector? (suppose relocation > does not happen ; maybe sectors exhausted) Does Linux receive the write > error upon the next flush it issues? At least for SCSI I believe the situation you describe is covered in the SCSI specifications as a deferred error. Basically, the device returns a check condition indicating a deferred failure in response to another command. My understanding (and I'm sure others can correct it) is that the device server can issue these check conditions anytime it wants. The only guarantee is that data written before the last successful SYNC is on the media (doesn't mean you can read it!). So, in order to guarantee data is not lost, a system using writeback should retain all of the writeback data until a successful SYNC CACHE operation. For example see, SPC4 4.5.7 note 6. If you consider what happens during power loss to a write-back cache, its the same situation. Bottom line, make sure to issue sync's for data you want to retain and use a filesystem/device that supports barriers and SYNC CACHE/CACHE FLUSH correctly. Still YMMV. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
