A month ago i had two drives fail long smart test Parity2 and Disk1. RMA-d the drives and bought new ones. During rebuild with the new ones ( both at the same time), one drooped out (Disk1), but parity2 disk Rebuild successfully. Then i rebuild parity Disk 1. Everything works fine for a day and then my Parity 1 is disabled (bought 3 disks in a batch 2 failed previously). New and old disks at some point were disabled, don't now the cause. Smart values are ok. Rebuilding parity for the third time. Can you take look at diagnostic files. First file is after rebuild of parity2 (disk1 disabled), and second is after parity was fully restored and then older drive is disabled (parity1). Thank you.

diskstation-diagnostics-20200608-2249.zip diskstation-diagnostics-20200611-1312.zip

Both diags are just after rebooting so we can't see what happened, next time grab them before rebooting, in the meantime you should upgrade the LSI firmware, latest is 20.00.07.00.

I upgraded firmware to (20.00.07.00) like you suggested. Parity disk again disabled. Giving you diagnostics before reboot, and smart values of the disk.

diskstation-diagnostics-20200804-0101.zip diskstation-smart-20200804-0108.zip

There are constant error like these on multiple devices:

 

Jul 28 00:08:15 Diskstation kernel: sd 7:0:6:0: Power-on or device reset occurred
Jul 28 00:08:21 Diskstation kernel: mpt2sas_cm0: log_info(0x31120303): originator(PL), code(0x12), sub_code(0x0303)
### [PREVIOUS LINE REPEATED 1 TIMES] ###
Jul 28 00:08:22 Diskstation kernel: sd 7:0:0:0: Power-on or device reset occurred
Jul 28 00:08:25 Diskstation kernel: mpt2sas_cm0: log_info(0x31120303): originator(PL), code(0x12), sub_code(0x0303)
### [PREVIOUS LINE REPEATED 7 TIMES] ###
Jul 28 00:08:26 Diskstation kernel: sd 7:0:6:0: Power-on or device reset occurred
Jul 28 00:08:45 Diskstation kernel: mpt2sas_cm0: log_info(0x31120303): originator(PL), code(0x12), sub_code(0x0303)
### [PREVIOUS LINE REPEATED 1 TIMES] ###
Jul 28 00:08:46 Diskstation kernel: sd 7:0:1:0: Power-on or device reset occurred
Jul 28 00:08:54 Diskstation kernel: mpt2sas_cm0: log_info(0x31120303): originator(PL), code(0x12), sub_code(0x0303)
### [PREVIOUS LINE REPEATED 4 TIMES] ###

 

Most like connections issue, could be SATA or power problem, so check/replace all cables, it could also be a failing PSU.