If it is a rotating rust drive I would run a full surface scan. If it is ab SSD I would take a close look at the detailed S.M.A.R.T. report.
I have a foot in both camps with a Fusion Drive. My "About this Mac" says:
Physical Volumes:
disk0s2:
Device Name: APPLE SSD SM0032L
Media Name: APPLE SSD SM0032L Media
Size: 27.55 GB (27,551,166,464 bytes)
Medium Type: SSD
Protocol: PCI-Express
Internal: Yes
Partition Map Type: GPT (GUID Partition Table)
Status: Online
PV UUID: 9A1E38C3-B6DF-462A-927F-90707416F920
disk1s2:
Device Name: APPLE HDD ST1000DM003
Media Name: APPLE HDD ST1000DM003 Media
Size: 999.35 GB (999,345,127,424 bytes)
Medium Type: Rotational
Protocol: SATA
Internal: Yes
Partition Map Type: GPT (GUID Partition Table)
Status: Online
S.M.A.R.T. Status: Verified
PV UUID: 50B19383-F528-492E-B3A4-2841AF4C391D
