Re:Debian-installer, mdadm configuration and the Bad Blocks ...
by grifferz on Wednesday September 16, 2020 @06:03AM
(#24491159)
As the article tries to state, the problem isn't that bad blocks can happen. The problems with md's bad blocks log are:
- Most of the time the entries don't correspond to actual bad blocks.
- It's buggy because it copies BBL between devices leading to another instance of "says the blocks are bad but they actually aren't"
- Once you've worked out that the entries are bogus it is still very hard to remove the entries or the BBL as a whole
- It's overly quiet in what it does. I monitor my syslogs but many people don't. There are many documented instances of people carrying entries in a BBL for years without knowing.
- Once MD thinks there is a bad block it renders that block on that device useless for recovery purposes. So in a two device array you just lost redundancy.
So this article has very little to do with the concept of bad blocks; it's about how md's BBL feature can be dangerous and why I don't want it enabled until it's fixed.
- Most of the time the entries don't correspond to actual bad blocks.
- It's buggy because it copies BBL between devices leading to another instance of "says the blocks are bad but they actually aren't"
- Once you've worked out that the entries are bogus it is still very hard to remove the entries or the BBL as a whole
- It's overly quiet in what it does. I monitor my syslogs but many people don't. There are many documented instances of people carrying entries in a BBL for years without knowing.
- Once MD thinks there is a bad block it renders that block on that device useless for recovery purposes. So in a two device array you just lost redundancy.
So this article has very little to do with the concept of bad blocks; it's about how md's BBL feature can be dangerous and why I don't want it enabled until it's fixed.