ATA errors in dmesg

Since a couple weeks, I sporadically find in dmesg a bunch of errors similar to the following one:

[174745.892138] ata7.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
[174745.892149] ata7.00: failed command: FLUSH CACHE EXT
[174745.892152] ata7.00: cmd ea/00:00:00:00:00/00:00:00:00:00/a0 tag 21
                         res 40/00:01:06:4f:c2/00:00:00:00:00/00 Emask 0x4 (timeout)
[174745.892163] ata7.00: status: { DRDY }
[174745.892169] ata7: hard resetting link
[174746.201093] ata7: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
[174746.218236] ata7.00: configured for UDMA/133
[174746.218245] ata7.00: retrying FLUSH 0xea Emask 0x4
[174746.218356] ata7: EH complete

It is always ata7 and it is always this same exception Emask. I already looked at the SMART data of all my disks, but they seem to be healthy, I cannot see any weird numbers under reallocated sectors count or something like this. I tried this answer here https://superuser.com/a/617193 to find out the actuyl sdX disk name, I get the following:

# grep '[0-9]' /sys/class/scsi_host/host{0..9}/unique_id
/sys/class/scsi_host/host0/unique_id:1
/sys/class/scsi_host/host1/unique_id:2
/sys/class/scsi_host/host2/unique_id:3
/sys/class/scsi_host/host3/unique_id:4
/sys/class/scsi_host/host4/unique_id:5
/sys/class/scsi_host/host5/unique_id:6
/sys/class/scsi_host/host6/unique_id:7
/sys/class/scsi_host/host7/unique_id:8
/sys/class/scsi_host/host8/unique_id:9
/sys/class/scsi_host/host9/unique_id:10

if I interpret this correctly, the disk ata7 belongs to SCSI Host 6? I then tried to find which disk is at host 6:

# ls -l /sys/block/sd*
lrwxrwxrwx 1 root root 0 Nov 24 19:28 /sys/block/sda -> ../devices/pci0000:00/0000:00:11.4/ata1/host0/target0:0:0/0:0:0:0/block/sda
lrwxrwxrwx 1 root root 0 Nov 24 19:28 /sys/block/sdb -> ../devices/pci0000:00/0000:00:11.4/ata2/host1/target1:0:0/1:0:0:0/block/sdb
lrwxrwxrwx 1 root root 0 Nov 24 19:28 /sys/block/sdc -> ../devices/pci0000:00/0000:00:11.4/ata3/host2/target2:0:0/2:0:0:0/block/sdc
lrwxrwxrwx 1 root root 0 Nov 24 19:28 /sys/block/sdd -> ../devices/pci0000:00/0000:00:11.4/ata4/host3/target3:0:0/3:0:0:0/block/sdd
lrwxrwxrwx 1 root root 0 Nov 24 19:28 /sys/block/sde -> ../devices/pci0000:00/0000:00:1f.2/ata5/host4/target4:0:0/4:0:0:0/block/sde
lrwxrwxrwx 1 root root 0 Nov 24 19:28 /sys/block/sdf -> ../devices/pci0000:00/0000:00:1f.2/ata6/host5/target5:0:0/5:0:0:0/block/sdf
lrwxrwxrwx 1 root root 0 Nov 24 19:28 /sys/block/sdg -> ../devices/pci0000:00/0000:00:1f.2/ata7/host6/target6:0:0/6:0:0:0/block/sdg

to me, it looks like the host 6 has disk sdg attached. However, when I check the SMART log of disk sdg, I cannot see anything that is dramatically different to all other disks, so I am wondering, are my above assumptions correct at all? and how can I find out what causes this strange errors in my dmesg? they seem to appear randomly, sometimes there are a few per hour, sometimes there is none for days. Is my disk dying and I just need to replace it, or is my hardware the problem? how can I isolate this? This is on a production system, so unfortunately it will not be so simple to randomly pull drives, change hardware or power off the system.