On Sun, Sep 21, 2008 at 10:26 AM, Nataraj incoming-centos@rjl.com 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,
No. Reads are distributed over disks to increase performance.
is whether bit errors that were somehow undetected by the hardware would be detected by the raid 1 software.
Depends on the type of error. However, the sad thing is, if you use 3 disks for raid 1 the kernel does not do the right thing. Let me explain.
Say you have 3 disks in a raid 1 array. If there is a mismatch then the smart thing to do would be to take a vote of the 3 disks. 2 out of 3 wins (assuming they are not all different). The odd man out should be corrected (if possible). But what actually happens is the highest numbered disk is copied to the others.
I haven't looked at the latest kernel code but if this http://linas.org/linux/raid.html is correct then I think the kernel maintainers should address this issue. I don't think it would be hard to implement.