[CentOS] question about software Raid 1

Sun Sep 21 18:12:17 UTC 2008
John R Pierce <pierce at hogranch.com>

Nataraj wrote:
> Does software raid 1 compare checksums or otherwise verify that the same
> bits are coming from both disks during reads?  What I'm interested in,
> is whether bit errors that were somehow undetected by the hardware would
> be detected by the raid 1 software.

under normal operation, each read request goes to one or the other 
drive, this doubles the read throughput as both drives can be servicing 
different read requests at the same time.

some raid does a scrub, where in the background, when the disks are 
otherwise idle, it gradually reads all the raid stripes and validates 
them.    I honestly don't know if Linux built in raid does this or 
not.   Of course, with RAID-1, if the two blocks disagree, there's no 
way of knowing which one is correct, only that there is a potential problem.

Some raid (Sun ZFS, for instance) stores a checksum with every block so 
it can detect corruption immediately.    Also, I know ZFS does this