Hi Everybody, I would like to propose a few probably hard-to-implement features to mdraid. Background: Nowadays harddisk drives, I only talk about ATA/SATA drives (SCSI devices are too expensive for me), do their own error correction. Most of them also have a feature called ERC (Error Recovery Control), where you can set timeouts for read/write error correction. Desktop drives are preset to run their error recovery to its fullest extend, not reacting while this procedure is active. RAID-edition/enterprise disks are normally set to start error recovery, but report back a media error after 7 seconds of unsuccessful error recovery - here this timeout "happens". Now imagine any RAID with some kind of redundancy, reading/writing data. One of the disks finds out "I cannot correctly read/write the requested sector", starts its error correction, hits the respective ERC-timeout and reports back a media error or unrecoverable error. Now mdraid would drop the disk. But actually the data of the sector can be recreated through the existing redundancy. Wouldn't it be a smart thing if the mdraid recreates the sector and just tried to write it again? And after a good amount of failed retries it may well drop the disk. Prerequisites: - upon assembling/creating of the array: - mdraid needs to find out if the used devices rely on (s)ata block devices - if it does, the ERC-timeouts for reading/writing operations on each device need to be set, as this feature is volatile (gets reset to factory defaults upon power-on-reset). - if successful, some flag indicating the enabled feature shall be set - error handling needs to be updated with above described "intelligence" for devices, that have the ERC-feature set This is a request for comments (and of course this feature). All the best, Stefan Hübner -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
