I've had a RAID1 setup running in my machine for a couple of years, and recently the array has become degraded. Looking at mdadm information, it looks like the one drive has failed, but when I look at SMART info, the other drive has had errors. I'm not sure which to trust.
If I'm reading the output of sudo mdadm --detail /dev/md0 correctly, /dev/sda1 has failed, and /dev/sdb1 is still in the array, and can be trusted.
/dev/md0:
Version : 1.2
Creation Time : Sat Jan 5 01:18:40 2013
Raid Level : raid1
Array Size : 2930133824 (2794.39 GiB 3000.46 GB)
Used Dev Size : 2930133824 (2794.39 GiB 3000.46 GB)
Raid Devices : 2
Total Devices : 1
Persistence : Superblock is persistent
Update Time : Thu Aug 6 20:33:11 2015
State : clean, degraded
Active Devices : 1
Working Devices : 1
Failed Devices : 0
Spare Devices : 0
Name : storm:0 (local to host storm)
UUID : 98b434f9:54d5c413:1acc4033:8ad34365
Events : 8388
Number Major Minor RaidDevice State
0 0 0 0 removed
1 8 17 1 active sync /dev/sdb1
However, after running a short SMART self-test on both drives, /dev/sda has no issues, but /dev/sdb is showing things like this:
=== START OF INFORMATION SECTION ===
Device Model: ST3000DM001-1CH166
...
Local Time is: Thu Aug 6 20:45:02 2015 EDT
SMART support is: Available - device has SMART capability.
SMART support is: Enabled
=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED
...
SMART Error Log Version: 1
ATA Error Count: 12 (device log contains only the most recent five errors)
...
Error 12 occurred at disk power-on lifetime: 21016 hours (875 days + 16 hours)
When the command that caused the error occurred, the device was active or idle.
After command completion occurred, registers were:
ER ST SC SN CL CH DH
-- -- -- -- -- -- --
40 51 00 ff ff ff 0f Error: UNC at LBA = 0x0fffffff = 268435455
Commands leading to the command that caused the error were:
CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name
-- -- -- -- -- -- -- -- ---------------- --------------------
60 00 00 ff ff ff 4f 00 8d+20:05:45.525 READ FPDMA QUEUED
ef 10 02 00 00 00 a0 00 8d+20:05:45.525 SET FEATURES [Reserved for Serial ATA]
27 00 00 00 00 00 e0 00 8d+20:05:45.525 READ NATIVE MAX ADDRESS EXT
ec 00 00 00 00 00 a0 00 8d+20:05:45.524 IDENTIFY DEVICE
ef 03 46 00 00 00 a0 00 8d+20:05:45.524 SET FEATURES [Set transfer mode]
...
SMART Self-test log structure revision number 1
Num Test_Description Status Remaining LifeTime(hours) LBA_of_first_error
# 1 Short offline Completed without error 00% 21129 -
# 2 Short offline Completed without error 00% 18418 -
# 3 Extended offline Completed without error 00% 1860 -
# 4 Short offline Completed without error 00% 1855 -
...
Full output can be found here: http://pastebin.com/jDN0muXk
Should I trust mdadm saying that /dev/sda is bad, and I should trust /dev/sdb, or should I trust SMART in /dev/sdb having errors, and /dev/sda still being in good shape?
