Diffrent between Online Spare and without online spare

[Paul_622]

What the different between Online Spare and not online spare? Example Raid5 with Online Spare and Raid5 without Online Spare.

[Marek Smejkal]

Paul,

online spare means, if there is disk failure in the Raid5, the spare disk automatically replace the failed one from the parity info other disks in the group. If there is another disk failure in the same group the data is still available.
Without online spare the first failure data accesible, the second failure, data lost.

Marek

[Greg Carlson]

Paul,

An online hot spare is a drive which is sitting and waiting to be rebuilt to incase you have a drive failure on an array to which that hotspare is dedicated to. This ensures that your array rebuild starts immediately to get you back into an optimal state until you can replace the failed hdd. Online spares are best on critical arrays and provides an extra level of protection. Obviously you'll still need to replace the failed hdd and at which point the controller will rebuild back to the original ID and the hotspare will return to a hot spare status.

The array w/out a hotspare will not start a rebuild process until you physically replace the hdd.

If the failure occurs over the weekend.. you'll be running degraded for 1-2 days on the array without a hot spare. The array with a hotspare will still be optimal.

Ciao,
Greg