Hi, I noticed the discussion about robust read on the RAID list and similar one on the EVMS list so I am sending this mail to both the lists. Latent media faults which prevent data from being read from portions of a disk has always been a concern for us. Such faults will go undetected till the time that block is read. RAID 1 depends on error free mirrors for proper operation and undiscovered bad blocks would only give pseudo illusion of duplexity when in reality the array should be degraded. Over long run all the mirrors might develop latent media faults and none can be replaced with a new disk. Also it is a disaster if the same block goes bad on all the mirrors in a RAID 1 volume. With this concern we developed what we call "disk-scrubber". The approach was to proactively seek for bad spots on the disk and when one is discovered, read the correct data from the other mirror and use it to repair the disk by way of a write. SCSI disks automatically repair bad spots on write by internally mapping the bad spots to spare sectors (Being SCSI centric might be one limitation of this solution). The implementation comprised of a thread that looks for bad spots by way of slow repeated continuous scan through all disks. The RAID error management was extended to attempt a repair on read error from a RAID 1 array to permit fixing of user discovered bad spots as well as those discovered by the scrubber. The work is lk2.4.26 based as of now. I can go back and put together a patch over the weekend if anyone is interested in using it. -dinesh dinesh.nagpure@xxxxxxxxxxx - 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
