Disk drive failure protection setting in Command View

[Simon R Wootton]

I have 3 disk groups within an EVA 8100 and have noticed that the above setting is different across the groups. Two groups have the setting on 'double', one on single.

I'd like to understand the setting in more detail if possible and also wonder if there is a 'threshold' (e.g. number of disks) at which it's better to adjust the setting.

All help appreciated and rewarded.
Simon

[Víctor Cespón · Accepted solution]

Hi, "Disk failure protection" parameter is an space that is reserved to rebuild the RAIDs in case a disk fails. This space is the equivalent of twice the size of the biggest disk on the disk group (Single) o 4 times (Double).

Check this document, page 10:
http://h71028.www7.hp.com/ERC/downloads/4AA0-2787ENW.pdf

Conversely, the statistical availability of disks and the typical service time to replace a failed disk (MTTR2) indicate that â doubleâ protection level is unnecessary in disk groups of fewer than 168 disks in all but the most conservative installations.