Re: [PERFORM] With 4 disks should I go for RAID 5 or RAID 10

On Wed, 26 Dec 2007, david@lang.hm 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(at)gregsmith.com 
http://www.gregsmith.com Baltimore, MD

---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend