raid-basics
Simple Volume - a single disk drive or segment; not redundant.
Spanned Volume - two or more disk drives or segments with the same or different capacity, connected end-to-end. A spanned volume offers no redundancy or performance advantage over a single drive.
RAID Volume - two or more logical drives with the same RAID level, connected end-to-end. The logical drives may have the same or different capacity and are not striped together; they may be redundant, depending on the RAID level.
RAID level-0 stripes the data across all the drives in the logical drive. This offers substantial speed enhancement but provides no data redundancy.
logical drive 12345678
physical drive 1 drive 2 1 2 3 4 5 6 7 8
RAID level-1 uses data mirroring. Two physical drives are combined into a logical drive, and data is striped across the logical drive. The first half of a stripe is the original data; the second half of a stripe is a mirror (that is, a copy) of the data, but it is written to the other drive in the RAID level-1 logical drive.
logical drive 1234 physical drive 1 drive2 1 1 2 2 3 3 4 4
RAID 1E is similar to RAID 5 with three drives but instead of a hotspare the data is running live and spread across all three.
RAID level-5 stripes data and parity across all drives in the logical drive. (minium requires 3 drives) Redundancy and performance
logical drive 12345678
physical drive 1 drive2 drive3 (hotspare)
* 1
2 *
* 3
4 *
On a failure the hotspare recreates the missing drive based on the * parity blocks.
DRIVE STATES
Okay: Logical Drive and underlying physical drives are working properly Critical: the Logical Drive contains a physical drive in an Offline or Defunct state. Degraded: one physical drive is defunct.
Offline: Drive is inaccessible (if Logical, may need to be rebuilt).
Ready: the physical drive awaiting definition (not part of a Logical Drive). Online: the physical drive is fine and participating in the Logical Drive. Hot spare: predefined physical drive awaiting use when a similar drive fails.
Defunct: doesn't respond to commands so the RAID controller cannot communicate properly.
Verifying: checking the drive for inconsistent or bad data. Rebuilding: the drive is being rebuilt.
Clearing: erases the first 1024 sectors (quick format) Impacted: error during synchronization