Raid6 Performance after one drive fails

[Martin-S]

Hi,
I´d like to know what happens with the performance of a Raid6 with HPE Smart Array P408i-a SR Gen10 Controller when one disk fails. Raid is degraded, but what about the performance?

Thanks,
Martin

[Jazz_ISS]

Hello Martin,

In Raid 6 when a hard drive fails and needs to be replaced it is, typically, hot-swapped out with a new hard drive. The controller card will initialize the new drive and begins to rebuild the data. Your OS/program should not even know you lost a harddrive.

RAID 6 protects data using double parity.
This makes it dramatically safer than RAID 5, but also imposes a dramatic write penalty.
Each write operation requires the disks to read the data, read the first parity, read the second parity, write the data, write the first parity and then finally write the second parity. This comes out to be a six times write penalty, which is pretty dramatic. 

Parity writes cause a very rapid decrease in write performance .