What is the “volume check” feature?
The feature called “volume check” in the Areca card interface tests the consistency of the RAID arrays. In doing so, all associated data blocks will be read, parity will be calculated, the stored parity read, and finally the calculated and stored parity values will be compared.
Naturally, the performance of the RAID set will be affected by this process. This is why we are recommending to run such a process during the nights or when the load on the DDP is the lowest.
Why volume check is needed?
During a volume check, all disks sectors are being read and written back. If no errors occur for a given sector, it is considered as usable. If an error occurs, the data block is being remapped to another sector that is believed to be stable. After the data is moved to another safe sector on the disk, the bad blocked is marked and not used anymore.
Another verification made during a volume check is the parity consistency check. This is also a critical step as if the parity data is incorrect, the original data cannot be recovered in case of read errors or disk failure.
Using a DDP with a faulty drive can result in many problems like client machines applications crashes, or lower performance among other things. This is why it is a so crucial maintenance tool to get the best of your DDP and prevent problems to occur.
Please refer to that topic in order to know how to run a volume check from the DDP web GUI.
How to see the volume check results?
You can simply go the “Raid cards” page from the DDP GUI, click on the RAID card you want to check and login to the Areca interface. (default login and password are admin/0000)
Then just go to the “View Events/Mute Beeper” section under the “System Controls” menu and check the log. Look to the “Time” and “Event Type” columns and locate the “Complete Check” lines as shown below:
This screenshot tells us that on August 31th, a volume check on the “r2″ RAID set completed with 2 errors.
Two conclusions can be made based on this information:
- The drive contained bad sectors, which means it’s losing its reliability and might indicate it is about to fail.
- Whenever the data had to be accessed and the error occurred in the past, the parity data has been needed to reconstruct the original data.
Although this last operation is transparent to the user, this is why performing volume checks regularly is important: when a bad sector is found, it is marked and the data block is remapped so that the read error cannot occur anymore on the same sector.
However remapping the blocks doesn’t mean that your drives are safe, it is best practice to perform a another volume check about one week after bad blocks have been marked. If the drive is about to fail, it is believed that more read errors will occur in the future, although this fact is nearly impossible to predict.
For users performing volume checks directly from the Areca web interface instead of the built-in “raid check” tool, please refer to the following topic as special cautions must be taken.