ZFS Pool is degrading alternately between two disks

[Binary.Coder]

Hi there,

I got a degraded status for the second disk of a pool, checked smart status and cleared it. A day later I got the status for the first disk:

ZFS has finished a scrub:

eid: 63
class: scrub_finish
host: pve
time: 2020-05-18 18:10:07+0200
pool: DiskPool
state: DEGRADED
status: One or more devices has experienced an unrecoverable error. An
attempt was made to correct the error. Applications are unaffected.
action: Determine if the device needs to be replaced, and clear the errors
using 'zpool clear' or replace the device with 'zpool replace'.
see: http://zfsonlinux.org/msg/ZFS-8000-9P
scan: scrub repaired 732K in 0 days 09:18:30 with 0 errors on Mon May 18 18:10:07 2020
config:

NAME STATE READ WRITE CKSUM
DiskPool DEGRADED 0 0 0
mirror-0 DEGRADED 0 0 0
sda DEGRADED 0 0 101 too many errors
sdc ONLINE 0 0 0

errors: No known data errors

The server and the disks are brand new and in usage now for about three months. No idea why this happens and what to do.

Kind regards,
Binary

 

[jim.bond.9862]

Well before anything else check your cables. A loose power or sas/sata cable to the disks will do that.
If not , and you are sure the disks are ok, it may be your PSU.

 

[Binary.Coder]

Cables seems ok. Got the following message :

This message was generated by the smartd daemon running on:

host name: pve
DNS domain: fritz.box

The following warning/error was logged by the smartd daemon:

Device: /dev/sda [SAT], 8 Currently unreadable (pending) sectors

Device info:
ST8000DM004-2CX188, S/N:XXXXX, WWN:5-000c50-0c330f7d9, FW:0001, 8.00 TB

For details see host's SYSLOG.

You can also use the smartctl utility for further investigation.
The original message about this issue was sent at Fri May 22 01:26:41 2020 CEST
Another message will be sent in 24 hours if the problem persists.

I think I should delegate this task to a professional, to figure out what is broken here.