I have a few hard drives in mdadm RAID 5 configured to go to standby after a few minutes of inactivity. (Using hdparm.conf spindown_time.)

At irregular intervals I get messages like these in dmesg:

[ 1840.251661] ata4.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
[ 1840.251722] ata4.00: failed command: SMART
[ 1840.251758] ata4.00: cmd b0/d5:01:06:4f:c2/00:00:00:00:00/00 tag 0 pio 512 in
[ 1840.251759]          res 40/00:14:50:2e:04/00:00:02:00:00/40 Emask 0x4 (timeout)
[ 1840.251858] ata4.00: status: { DRDY }
[ 1840.251888] ata4: hard resetting link
[ 1840.600742] ata4: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
[ 1840.601521] ata4.00: configured for UDMA/133
[ 1840.601547] ata4: EH complete
[337877.713988] ata4.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
[337877.714019] ata4.00: failed command: SMART
[337877.714038] ata4.00: cmd b0/d5:01:06:4f:c2/00:00:00:00:00/00 tag 0 pio 512 in
[337877.714039]          res 40/00:04:90:10:81/00:00:00:00:00/40 Emask 0x4 (timeout)
[337877.714089] ata4.00: status: { DRDY }
[337877.714107] ata4: hard resetting link
[337878.063085] ata4: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
[337878.063743] ata4.00: configured for UDMA/133
[337878.063764] ata4: EH complete

I think the exception is caused by smartd when a drive does not wake up quickly enough.

There are no issues (that I can tell) in accessing the drives normally through the file system - it takes a few seconds longer than normal when they are asleep, but there are no exceptions.

Is this something I should worry about, as a potential symptom on something that could corrupt a drive over time?

Or can I safely ignore it as part of normal operation?

Edit:

By request: smartctl -a for sdaand sde, both disks are members of the array.

If ata4is the same as scsi-4 then sde is the one that gave the error above, according to /dev/disk/by-path.