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

[Greg Smith <gsmith(at)gregsmith(dot)com>]

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