On Wed, 26 Dec 2007, david@xxxxxxx wrote:
yes, the two linux software implementations only read from one disk, but I have seen hardware implementations where it reads from both drives, and if they disagree it returns a read error rather then possibly invalid data (it's up to the admin to figure out which drive is bad at that point).
Right, many of the old implementations did that; even the Wikipedia article on this subject mentions it in the "RAID 1 performance" section: http://en.wikipedia.org/wiki/Standard_RAID_levels
The thing that changed is on modern drives, the internal error detection and correction is good enough that if you lose a sector, the drive will normally figure that out at the firmware level and return a read error rather than bad data. That lowers of the odds of one drive becoming corrupted and returning a bad sector as a result enough that the overhead of reading from both drives isn't considered as important. I'm not aware of a current card that does that but I wouldn't be surprised to discover one existed.
-- * Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
