lost all share access

From your diagnostics.log:

Disks
-------------------------------
* Disk 0 (model Seagate ST31000340NS) has 1094 reallocated sectors.  Reallocated sectors might be acceptable, but they are often the first warning sign that a disk is starting to fail.
* Disk 0 (model Seagate ST31000340NS) has 115 ATA errors.  ATA errors are logged when the disk fails to complete an internal command.  This can be a sign that the disk is starting to fail.
* Disk 1 (model Seagate ST31000340NS) has 45 reallocated sectors.  Reallocated sectors might be acceptable, but they are often the first warning sign that a disk is starting to fail.
* Disk 1 (model Seagate ST31000340NS) has 48 ATA errors.  ATA errors are logged when the disk fails to complete an internal command.  This can be a sign that the disk is starting to fail.
* Disk 4 (model Seagate ST31000340NS) has 12 ATA errors.  ATA errors are logged when the disk fails to complete an internal command.  This can be a sign that the disk is starting to fail.

So Disk 0 is bad, Disk 1 and disk 4 maybe as well. disk_smart.log has more details

(Or disk 1,2 and 5 if you count from 1-6).

Looking at status-old.log I see lots of warnings about the bad disk.

Also I see you do RAID scrubbing? How often do you do that? Note that with failing disks, the stress of a resync can finish disks off.

I see you are using X-RAID2 dual-redundancy (like RAID-6).

I am convinced that the weird behaviour of your system with samba not starting is probably related to your problem disk(s).

We generally recommend replacing disks once either the reallocated sector count or ATA error count reaches 50.

Other counts such as a non-zero Current Pending Sector count also can indicate a problem.

Do you have a backup?