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I am running a CentOS 7 machine (standard kernel: 3.10.0-327.36.3.el7.x86_64) with a software RAID-10 over 16x 1 TB SSDs (to be more precise, there are two RAID arrays on the disks; one of the arrays is providing the host's swap partition). Last week, a SSD failed:

13:18:07 kvm7 kernel: sd 1:0:2:0: attempting task abort! scmd(ffff887e57b916c0)
13:18:07 kvm7 kernel: sd 1:0:2:0: [sdk] CDB: Write(10) 2a 08 02 55 20 08 00 00 01 00
13:18:07 kvm7 kernel: scsi target1:0:2: handle(0x000b), sas_address(0x4433221102000000), phy(2)
13:18:07 kvm7 kernel: scsi target1:0:2: enclosure_logical_id(0x500304801c14a001), slot(2)
13:18:10 kvm7 kernel: sd 1:0:2:0: task abort: SUCCESS scmd(ffff887e57b916c0)
13:18:11 kvm7 kernel: sd 1:0:2:0: [sdk] FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
13:18:11 kvm7 kernel: sd 1:0:2:0: [sdk] Sense Key : Not Ready [current] 
13:18:11 kvm7 kernel: sd 1:0:2:0: [sdk] Add. Sense: Logical unit not ready, cause not reportable
13:18:11 kvm7 kernel: sd 1:0:2:0: [sdk] CDB: Write(10) 2a 08 02 55 20 08 00 00 01 00
13:18:11 kvm7 kernel: blk_update_request: I/O error, dev sdk, sector 39133192
13:18:11 kvm7 kernel: blk_update_request: I/O error, dev sdk, sector 39133192
13:18:11 kvm7 kernel: md: super_written gets error=-5, uptodate=0
13:18:11 kvm7 kernel: md/raid10:md3: Disk failure on sdk3, disabling device.#012md/raid10:md3: Operation continuing on 15 devices.
13:19:27 kvm7 kernel: sd 1:0:2:0: device_blocked, handle(0x000b)
13:19:29 kvm7 kernel: sd 1:0:2:0: [sdk] Synchronizing SCSI cache
13:19:29 kvm7 kernel: md: md3 still in use.
13:19:29 kvm7 kernel: sd 1:0:2:0: [sdk] Synchronize Cache(10) failed: Result: hostbyte=DID_NO_CONNECT driverbyte=DRIVER_OK
13:19:29 kvm7 kernel: mpt3sas1: removing handle(0x000b), sas_addr(0x4433221102000000)
13:19:29 kvm7 kernel: md: md2 still in use.
13:19:29 kvm7 kernel: md/raid10:md2: Disk failure on sdk2, disabling device.#012md/raid10:md2: Operation continuing on 15 devices.
13:19:29 kvm7 kernel: md: unbind<sdk3>
13:19:29 kvm7 kernel: md: export_rdev(sdk3)
13:19:29 kvm7 kernel: md: unbind<sdk2>
13:19:29 kvm7 kernel: md: export_rdev(sdk2)

/proc/mdstat looked as expected (1 faulty member) and the VMs kept running without any problems.

md3 : active raid10 sdp3[15] sdb3[2] sdg3[12] sde3[8] sdn3[11] sdl3[7] sdm3[9] sdf3[10] sdi3[1] sdk3[5](F) sdc3[4] sdd3[6] sdh3[14] sdo3[13] sda3[0] sdj3[3]
  7844052992 blocks super 1.2 128K chunks 2 near-copies [16/15] [UUUUU_UUUUUUUUUU]

The SSD had to be temporarily replaced with a bigger SSD as no 1 TB SSD was available; so we did, started the rebuild and everything was fine. Today the "right" SSD arrived, so the datacenter technican just pulled the tray containing the mentioned SSD and the system became unresponsive within seconds. While the host was running fine on a seperated RAID array, the VMs were unable to perform I/O. The load increased to > 800. I was able to execute mdadm --detail /dev/md3 which showed a degraded (but active / clean) array, so from this point of view the system was absolutely fine. I tried to remove the faulty / missing drive from the array, which of course failed ("no such device"), and suddenly even mdadm --detail /dev/md3 didn't generate any output anymore, it simply stuck and I had to kill the SSH session to get out of this. After this, I decided to force a reboot as I didn't even know how to remove this faulty drive from the array - and everything came up correctly. Of course the RAID was still degraded and needed a resync, but apart from that: no problems.

I'm pretty sure that I should have removed the drive via mdadm after a --set-faulty before pulling the tray out of the rack, though I can't explain this behaviour of mdraid. In my opinion we "simulated" a regular disk outage, so has anybody an idea what caused this issue and how I can make sure, that the next regular disk outage won't cause the same problem?

The kernel logged some messages, and what I find interesting is that the new device came up as sdq while the pulled device was known as sdk. So I assume that sdk was not kicked correctly from the array. When the initial SSD failure happened last week, I didn't see this behaviour; so the replacement drive also came up as sdk.

The log also shows 7 minutes between the failure of the old and the insertion of the new SSD, so I don't think that a problem like it was described under https://superuser.com/questions/942886/fail-device-in-md-raid-when-ata-stops-responding took place. Also the VMs went down immediately and not 7 minutes later. So - any thoughts on that? Would be greatly appreciated :)

11:45:36 kvm7 kernel: sd 1:0:8:0: device_blocked, handle(0x000b)
11:45:37 kvm7 kernel: blk_update_request: I/O error, dev sdk, sector 0
11:45:37 kvm7 kernel: md/raid10:md3: sdk3: rescheduling sector 4072069640
11:45:37 kvm7 kernel: md/raid10:md3: sdk3: rescheduling sector 4072069648
11:45:37 kvm7 kernel: md/raid10:md3: sdk3: rescheduling sector 4072069656
11:45:37 kvm7 kernel: md/raid10:md3: sdk3: rescheduling sector 4072069664
11:45:37 kvm7 kernel: md/raid10:md3: sdk3: rescheduling sector 4072069672
11:45:37 kvm7 kernel: md/raid10:md3: sdk3: rescheduling sector 4072069680
11:45:37 kvm7 kernel: md/raid10:md3: sdk3: rescheduling sector 4072069688
11:45:37 kvm7 kernel: md/raid10:md3: sdk3: rescheduling sector 4072069696
11:45:37 kvm7 kernel: md/raid10:md3: sdk3: rescheduling sector 4072069704
11:45:37 kvm7 kernel: md/raid10:md3: sdk3: rescheduling sector 4072069712
11:45:37 kvm7 kernel: sd 1:0:8:0: [sdk] FAILED Result: hostbyte=DID_NO_CONNECT driverbyte=DRIVER_OK
11:45:37 kvm7 kernel: sd 1:0:8:0: [sdk] CDB: Read(10) 28 00 20 af f7 08 00 00 08 00
11:45:37 kvm7 kernel: blk_update_request: I/O error, dev sdk, sector 548402952
11:45:37 kvm7 kernel: blk_update_request: I/O error, dev sdk, sector 0
11:45:37 kvm7 kernel: blk_update_request: I/O error, dev sdk, sector 39133192
11:45:37 kvm7 kernel: md: super_written gets error=-5, uptodate=0
11:45:37 kvm7 kernel: md/raid10:md3: Disk failure on sdk3, disabling device.#012md/raid10:md3: Operation continuing on 15 devices.
11:45:37 kvm7 kernel: md: md2 still in use.
11:45:37 kvm7 kernel: md/raid10:md2: Disk failure on sdk2, disabling device.#012md/raid10:md2: Operation continuing on 15 devices.
11:45:37 kvm7 kernel: blk_update_request: I/O error, dev sdk, sector 39133264
11:45:37 kvm7 kernel: md: super_written gets error=-5, uptodate=0
11:45:37 kvm7 kernel: sd 1:0:8:0: [sdk] Synchronizing SCSI cache
11:45:37 kvm7 kernel: sd 1:0:8:0: [sdk] Synchronize Cache(10) failed: Result: hostbyte=DID_NO_CONNECT driverbyte=DRIVER_OK
11:45:37 kvm7 kernel: mpt3sas1: removing handle(0x000b), sas_addr(0x4433221102000000)
11:45:37 kvm7 kernel: md: unbind<sdk2>
11:45:37 kvm7 kernel: md: export_rdev(sdk2)
11:48:00 kvm7 kernel: INFO: task md3_raid10:1293 blocked for more than 120 seconds.
11:48:00 kvm7 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
11:48:00 kvm7 kernel: md3_raid10      D ffff883f26e55c00     0  1293      2 0x00000000
11:48:00 kvm7 kernel: ffff887f24bd7c58 0000000000000046 ffff887f212eb980 ffff887f24bd7fd8
11:48:00 kvm7 kernel: ffff887f24bd7fd8 ffff887f24bd7fd8 ffff887f212eb980 ffff887f23514400
11:48:00 kvm7 kernel: ffff887f235144dc 0000000000000001 ffff887f23514500 ffff8807fa4c4300
11:48:00 kvm7 kernel: Call Trace:
11:48:00 kvm7 kernel: [<ffffffff8163bb39>] schedule+0x29/0x70
11:48:00 kvm7 kernel: [<ffffffffa0104ef7>] freeze_array+0xb7/0x180 [raid10]
11:48:00 kvm7 kernel: [<ffffffff810a6b80>] ? wake_up_atomic_t+0x30/0x30
11:48:00 kvm7 kernel: [<ffffffffa010880d>] handle_read_error+0x2bd/0x360 [raid10]
11:48:00 kvm7 kernel: [<ffffffff812c7412>] ? generic_make_request+0xe2/0x130
11:48:00 kvm7 kernel: [<ffffffffa0108a1d>] raid10d+0x16d/0x1440 [raid10]
11:48:00 kvm7 kernel: [<ffffffff814bb785>] md_thread+0x155/0x1a0
11:48:00 kvm7 kernel: [<ffffffff810a6b80>] ? wake_up_atomic_t+0x30/0x30
11:48:00 kvm7 kernel: [<ffffffff814bb630>] ? md_safemode_timeout+0x50/0x50
11:48:00 kvm7 kernel: [<ffffffff810a5b8f>] kthread+0xcf/0xe0
11:48:00 kvm7 kernel: [<ffffffff810a5ac0>] ? kthread_create_on_node+0x140/0x140
11:48:00 kvm7 kernel: [<ffffffff81646a98>] ret_from_fork+0x58/0x90
11:48:00 kvm7 kernel: [<ffffffff810a5ac0>] ? kthread_create_on_node+0x140/0x140
11:48:00 kvm7 kernel: INFO: task qemu-kvm:26929 blocked for more than 120 seconds.

[serveral messages for stuck qemu-kvm processes]

11:52:42 kvm7 kernel: scsi 1:0:9:0: Direct-Access     ATA      KINGSTON SKC400S 001A PQ: 0 ANSI: 6
11:52:42 kvm7 kernel: scsi 1:0:9:0: SATA: handle(0x000b), sas_addr(0x4433221102000000), phy(2), device_name(0x4d6b497569a68ba2)
11:52:42 kvm7 kernel: scsi 1:0:9:0: SATA: enclosure_logical_id(0x500304801c14a001), slot(2)
11:52:42 kvm7 kernel: scsi 1:0:9:0: atapi(n), ncq(y), asyn_notify(n), smart(y), fua(y), sw_preserve(y)
11:52:42 kvm7 kernel: scsi 1:0:9:0: qdepth(32), tagged(1), simple(0), ordered(0), scsi_level(7), cmd_que(1)
11:52:42 kvm7 kernel: sd 1:0:9:0: Attached scsi generic sg10 type 0
11:52:42 kvm7 kernel: sd 1:0:9:0: [sdq] 2000409264 512-byte logical blocks: (1.02 TB/953 GiB)
11:52:42 kvm7 kernel: sd 1:0:9:0: [sdq] Write Protect is off
11:52:42 kvm7 kernel: sd 1:0:9:0: [sdq] Write cache: enabled, read cache: enabled, supports DPO and FUA
11:52:42 kvm7 kernel: sdq: unknown partition table
11:52:42 kvm7 kernel: sd 1:0:9:0: [sdq] Attached SCSI disk
  • What's interesting to me is that there's an md: unbind<sdk2> but no md: unbind<sdk3> so it does seem that you are right that the drive didn't get properly removed from the array but I don't know why. – DerfK Dec 16 '16 at 18:29
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From the kernel stack trace, it seems that the md driver tried to freeze the array (freeze_array+0xb7/0x180 [raid10]) to completely remove the failed member, but this operation never completed. This is confirmed by the missing md: unbind<sdk3> line.

To me, it seems a dead/live lock problem, so the root cause can be a software bug. You should really submit a report on the Linux RAID mailing list

  • We reported the issue in the mailing list and found out that this is a known bug / deadlock in freeze_array. It should be fixed soon, but the developers do not know how the CentOS developers handle this. We switched to an "original" kernel. – smartenbergen Jan 13 '17 at 13:50
  • Interesting. Can you reference the mailing list thread for future readers? – shodanshok Jan 13 '17 at 15:20

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