Hello, I've got some bad sectors on one drive: dd: reading `/dev/sdh1': Input/output error 260200+0 records in 260200+0 records out 133222400 bytes (133 MB) copied, 2.97188 s, 44.8 MB/s [ 3908.350331] ata9.00: exception Emask 0x0 SAct 0x40000 SErr 0x0 action 0x0 [ 3908.350385] ata9.00: irq_stat 0x40000008 [ 3908.350427] ata9.00: failed command: READ FPDMA QUEUED [ 3908.350474] ata9.00: cmd 60/06:90:6a:00:04/00:00:00:00:00/40 tag 18 ncq 3072 in [ 3908.350474] res 51/40:06:6a:00:04/00:00:00:00:00/40 Emask 0x409 (media error) <F> [ 3908.350628] ata9.00: status: { DRDY ERR } [ 3908.350669] ata9.00: error: { UNC } [ 3908.354643] ata9.00: configured for UDMA/133 [ 3908.354664] sd 8:0:0:0: [sdh] Unhandled sense code [ 3908.354668] sd 8:0:0:0: [sdh] [ 3908.354671] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE [ 3908.354674] sd 8:0:0:0: [sdh] [ 3908.354677] Sense Key : Medium Error [current] [descriptor] [ 3908.354681] Descriptor sense data with sense descriptors (in hex): [ 3908.354683] 72 03 11 04 00 00 00 0c 00 0a 80 00 00 00 00 00 [ 3908.354695] 00 04 00 6a [ 3908.354701] sd 8:0:0:0: [sdh] [ 3908.354705] Add. Sense: Unrecovered read error - auto reallocate failed [ 3908.354708] sd 8:0:0:0: [sdh] CDB: [ 3908.354710] Read(10): 28 00 00 04 00 6a 00 00 06 00 [ 3908.354721] end_request: I/O error, dev sdh, sector 262250 [ 3908.354773] Buffer I/O error on device sdh1, logical block 260202 [ 3908.354825] Buffer I/O error on device sdh1, logical block 260203 [ 3908.354891] Buffer I/O error on device sdh1, logical block 260204 [ 3908.354942] Buffer I/O error on device sdh1, logical block 260205 [ 3908.354992] Buffer I/O error on device sdh1, logical block 260206 [ 3908.355042] Buffer I/O error on device sdh1, logical block 260207 [ 3908.355125] ata9: EH complete Generally I believe these should go away when overwritten, but how do I overwrite them? The drive is an md RAID1 member: /dev/md4: Version : 1.2 Creation Time : Mon May 26 13:40:18 2014 Raid Level : raid1 Array Size : 1953379936 (1862.89 GiB 2000.26 GB) Used Dev Size : 1953379936 (1862.89 GiB 2000.26 GB) Raid Devices : 2 Total Devices : 2 Persistence : Superblock is persistent Intent Bitmap : Internal Update Time : Sun Feb 8 02:39:58 2015 State : active Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 Name : natsu.romanrm.net:4 (local to host natsu.romanrm.net) UUID : 3b8c3166:073249b5:e1384bd6:4611df90 Events : 50426 Number Major Minor RaidDevice State 0 8 49 0 active sync /dev/sdd1 1 8 113 1 active sync /dev/sdh1 I thought I would run a 'check' or 'repair', this will read from both drives, fail to read from sdh, then try to overwrite the affected areas on sdh. But nope: # echo 0 > /sys/block/md4/md/sync_min # echo check > /sys/block/md4/md/sync_action [ 4059.451036] md: data-check of RAID array md4 [ 4059.451040] md: minimum _guaranteed_ speed: 1000 KB/sec/disk. [ 4059.451042] md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for data-check. [ 4059.451046] md: using 128k window, over a total of 1953379936k. This happily proceeds through the supposedly unreadable area: md4 : active raid1 sdd1[0] sdh1[1] 1953379936 blocks super 1.2 [2/2] [UU] [>....................] check = 0.0% (1479680/1953379936) finish=1116.8min speed=29128K/sec bitmap: 2/8 pages [8KB], 131072KB chunk at 1.5GB already, while the unreadable sectors are at ~133MB. And no new ATA errors in dmesg. How is this possible? If I retry the 'dd' command right now, it fails exactly in the same way as before (and ATA errors do indeed appear). -- With respect, Roman -- 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