Hi all, I am running software RAID on Linux 2.6.21. While experimenting with adding and removing devices from the RAID array, I noticed something very troubling. I have a bad drive (let's call it drive B) which gets random read errors. I also have a good drive, call it drive A. B can synchronize with A. But then, if I remove A from the raid array, A cannot be re-added. This is because the bad drive, B, cannot be read from. Basically, B appears to be "write-only"; it will never return an error on a write, but just try to read from it, and you will be sorry. Writing is fine: [root@cmccabe-devel root]# dd if=/dev/zero of=/dev/sdb bs=524288 dd: writing `/dev/sdb': No space left on device 114464+0 records in 114463+0 records out Reading is not: [root@cmccabe-devel root]# dd if=/dev/sdb of=/dev/null bs=524288 ata1.00: exception Emask 0x0 SAct 0x3 SErr 0x0 action 0x2 frozen ata1.00: cmd 60/00:00:00:b0:01/01:00:00:00:00/40 tag 0 cdb 0x0 data 131072 in [ ... copious errors ... ] I have disabled write caching using hdparm -W0. Both drives are: Fujitsu MHV2060BH, 60 GB, Serial ATA The SATA controller is: ICH6 My problem is that even though B gets into the synchronized state, it is no good at all. This is potentially misleading, and if someone removes A after synchronizing B, the system will probably crash, since there will be no good drives left. I wonder if anyone else is interested in a "paranoid recovery" mode where the md layer tests the data that has been written. Even if this doubles the recovery time, I think that it would be desirable for many applications. Colin - 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
