Is my hard drive already dying? Although everything is working fine with my Macbook Air from Mid-2013, I have a few errors that bother me.

Here they are:

Onyx says this:


  The SMART status was not verified because it is not supported by this hard disk.


But the system report writes this:

disk0s2:
  Media Name:   APPLE SSD SD0256F Media
  Size: 250,14 GB (250 140 434 432 bytes)
  Medium Type:  SSD
  Protocol: PCI
  Internal: Yes
  Partition Map Type:   GPT (GUID Partition Table)
  Status:   Online
  S.M.A.R.T. Status:    Verified
  PV UUID:  4F6EBACC-CA60-4DE6-95BF-37F42D820284


After installing smartmontools:

smartctl disk1 -a  
SMART support is: Available - device has SMART capability. 
SMART support is: Enabled  
=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED 


So SMART seems good, maybe onyx is in fault. But my cksum mismatch problem is still here

When I run disk utility and I perform a verification on my hard drive I always get this:


  Invalid Disk Label @ 250123653120: cksum mismatch


And sometimes if I wait enough time (a few days) after a repair (with the cmd+R on boot utility) I get this kind of error:
Incorrect block count for file (...)

This last problem seems to happen with files I downloaded and most likely which I didn't finish to download.

What I think:
When Yosemite came out I installed it, but since I found that even resizing a window wasn't as smooth as on Mavericks I decided to downgrade using my Time Machine backup.

Do you think upgrading back to Yosemite would fix all this? And would I still find this kind of performance?

Edit: If it is a good idea, I have no problem with doing a clean install of Yosemite.

Thanks in advance for your help. My Mac is still young and I don't want him to be sick.
You file system is corrupted, hardware is probably fine. Backup, wipe and restore.