From what you describe, the first drive is defective. Read Error Rate and Re-allocated Sector Sount are non-zero. Re-allocating sectors is exactly what happens when the drive can not read a sector. It will then re-allocate this sector on the next write operation.

You can do several things to confirm this diagnosis:

Simple but uncertain: use a tool like HDD Scan to scan your disk, i.e., read every sector from your disk. You can also do this operation on your RAID 1 array. But than it is up to the RAID-firmware to decide if it will read the data from disk 1 oder disk 2. Therefore this method will not check every sector on both disks. But if disk 1 is about to fail, it is quite probable (but not guaranteed), that its SMART values will worsen.

Keep an eye on Re-allocated Sector Sount, Reallocation Event Count and Current Pending Sector Count. If these values go up, your drive is likely to fail soon.

Complicated but gives more certainty:

1. Mount your drives in a different pc/usb-enclosure/different SATA-port.
2. Boot from a Live CD (e.g. Ubuntu or Knoppix).
3. Perform a read only test of your drives. You can do this by SMART commands and/or by using tools like dd or badblocks

• do NOT attempt to mount the filesystem
• do NOT write anything to the drive
• when you do read-only operations, you can re-assemble the RAID without it beeing marked as faulty/inconsistent.

1. Keep an eye on the same values as mentioned above. Now you should also be able to read the SMART values properly. SMART usually also has a log about previous errors that happened. Drive 1 hat at least two of them. The timestamp is usually expressed as power-on-hours. So you will have to calculate back from the current power-on-hours and see if this correlates with the time you experienced the problems.

From what you describe, the first drive is defective. Read Error Rate and Re-allocated Sector Count are non-zero. Re-allocating sectors is exactly what happens when the drive can not read a sector. It will then re-allocate this sector on the next write operation.

You can do several things to confirm this diagnosis:

Simple but uncertain: use a tool like HDD Scan to scan your disk, i.e., read every sector from your disk. You can also do this operation on your RAID 1 array. But than it is up to the RAID-firmware to decide if it will read the data from disk 1 oder disk 2. Therefore this method will not check every sector on both disks. But if disk 1 is about to fail, it is quite probable (but not guaranteed), that its SMART values will worsen.

Keep an eye on Re-allocated Sector Count, Reallocation Event Count and Current Pending Sector Count. If these values go up, your drive is likely to fail soon.

Complicated but gives more certainty:

1. Mount your drives in a different pc/usb-enclosure/different SATA-port.
2. Boot from a Live CD (e.g. Ubuntu or Knoppix).
3. Perform a read only test of your drives. You can do this by SMART commands and/or by using tools like dd or badblocks

• do NOT attempt to mount the filesystem
• do NOT write anything to the drive
• when you do read-only operations, you can re-assemble the RAID without it beeing marked as faulty/inconsistent.

1. Keep an eye on the same values as mentioned above. Now you should also be able to read the SMART values properly. SMART usually also has a log about previous errors that happened. Drive 1 hat at least two of them. The timestamp is usually expressed as power-on-hours. So you will have to calculate back from the current power-on-hours and see if this correlates with the time you experienced the problems.