Hello everyone, an update: I was able to reproduce the problem on my testing machine (at least sort of) and confirmed that c8dc9c6 md: raid1,10: Handle REQ_WRITE_SAME flag in write bios fixes things. Also applied c8dc9c6 to the main system's 3.8.6 kernel. Working without any issues. One interesting detail: on the testing system's 9240-8i lsi controller (megaraid_sas instead of mpt2sas driver) the log messages where different and seemingly not coming from controller errors: Apr 9 12:59:17 kernel: bio too big device sdb (4096 > 256) Apr 9 12:59:17 kernel: md12: WRITE SAME failed. Manually zeroing. Whereas the lsi 9211-8i gave these messages: [ 2772.726292] mpt2sas0: log_info(0x31120320): originator(PL), code(0x12), sub_code(0x0320) [ 2772.726296] mpt2sas0: log_info(0x31120320): originator(PL), code(0x12), sub_code(0x0320) [ 2772.940873] mpt2sas0: log_info(0x31120320): originator(PL), code(0x12), sub_code(0x0320) [ 2773.205568] mpt2sas0: log_info(0x31120320): originator(PL), code(0x12), sub_code(0x0320) [ 2773.953718] mpt2sas0: log_info(0x31120320): originator(PL), code(0x12), sub_code(0x0320) [ 2774.203121] mpt2sas0: log_info(0x31120320): originator(PL), code(0x12), sub_code(0x0320) [ 2774.452462] mpt2sas0: log_info(0x31120320): originator(PL), code(0x12), sub_code(0x0320) [ 2774.452476] sd 0:0:4:0: [sde] Unhandled error code [ 2774.452479] sd 0:0:4:0: [sde] [ 2774.452480] Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK [ 2774.452482] sd 0:0:4:0: [sde] CDB: [ 2774.452483] Write(10): 2a 00 a9 84 24 08 00 00 08 00 [ 2774.452491] end_request: I/O error, dev sde, sector 2844009480 [ 2774.452636] md3: WRITE SAME failed. Manually zeroing. The former one looks a lot more friendly to me. @lsi guys: this reveals a bug in the mpt2sas driver and/or the 9211&co series firmware, correct? Thanks everyone for your help so far, Matthias -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html