In short: smartctl lists one pending sector. A dd of that disk provokes an i/o error as expected. A raid 'sync_action=check' does not find a problem and does *not* trigger an i/o error. Why? My smart log is indicating a pending sector in a component of a 7x4TB (software) raid6 device. Looking at that component I see: # smartctl -x /dev/sdi ... 197 Current_Pending_Sector -O--CK 200 200 000 - 1 ... SMART Extended Self-test Log Version: 1 (1 sectors) Num Test_Description Status Remaining LifeTime(hours) LBA_of_first_error # 1 Short offline Completed: read failure 90% 5878 261696 ... I then test this by attempting to read around the bad sector: # dd if=/dev/sdi of=/dev/null skip=261120 count=2048 dd: error reading '/dev/sdi': Input/output error 576+0 records in 576+0 records out 294912 bytes (295 kB) copied, 3.18338 s, 92.6 kB/s and the log shows: # dmesg|tail [768141.382189] 72 03 11 04 00 00 00 0c 00 0a 80 00 00 00 00 00 [768141.461997] 00 03 fe 40 [768141.503122] sd 6:0:6:0: [sdi] [768141.542668] Add. Sense: Unrecovered read error - auto reallocate failed [768141.623913] sd 6:0:6:0: [sdi] CDB: [768141.667622] Read(16): 88 00 00 00 00 00 00 03 fe 40 00 00 00 08 00 00 [768141.748586] end_request: I/O error, dev sdi, sector 261696 [768141.816217] Buffer I/O error on device sdi, logical block 32712 [768141.889061] ata13: EH complete [768141.927696] sas: --- Exit sas_scsi_recover_host: busy: 0 failed: 0 tries: 1 I ran a raid check Feb 21 00:05:01 e7 kernel: [815562.730457] md: data-check of RAID array md127 Feb 21 00:05:01 e7 kernel: [815562.745190] md: minimum _guaranteed_ speed: 100000 KB/sec/disk. Feb 21 00:05:01 e7 kernel: [815562.764583] md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for data-check. Feb 21 00:05:01 e7 kernel: [815562.795202] md: using 128k window, over a total of 3906885120k. Feb 21 09:48:28 e7 kernel: [850585.930844] md: md127: data-check done. It did not find any problem and did not trigger an i/o error, and the final mismatch_count=0. Neither was the pending cluster reallocated (which would happen if it was written to by the raid6 if it saw a read i/o error, I think). Q1) Why do I *not* see an i/o error from the raid check? Q2) Do we have a writeup on how to translate the sector (in the i/o error) to a block in the raid device (/dev/mdN)? Here is how I see it: I know that /dev/sdi1 starts 2048 sectors into the disk (call it 256 4k blocks). Being a 7 disk raid6 means that this block (n=32712-256=32456) is seen by the fs near block (b=n*5=162280) and this [n,...,n+4] is the block number to use to start tracing with debugfs. I do assume that my ext4 also uses 4k blocks. I still have the pending sector and am ready to experiment (up to a point...). TIA -- Eyal Lebedinsky (eyal@xxxxxxxxxxxxxx) -- 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
