Re: md failing mechanism

[James J <james.j@shiftmail.org>]

On 23/01/2016 15:09, Wols Lists wrote:
> On 22/01/16 23:40, James J wrote:
>> The recommentation of raising the timeout to 120+ is for the opposite
>> purpose of what you want. It is for the case the sysadmin accepts to
>> wait a long time because he wants to prevent the kicking of the drive at
>> the first read-error (normally drives are kicked for a write error).
>> This might be wanted in order to a) defer the replacement of the drive,
>> either to perform the replacement at a more opportune time and/or in a
>> better manner such as a no-degrade replace operation, or b) because he
>> does not want to replace the drive at all: maybe he believes that the
>> error might be spurious and will not happen again and the drive is still
>> of acceptable fitness for the purpose, e.g. in a low-cost file server.
> Except, aiui, even in your scenario! drives are kicked for a *write* error.
>
> What happens (should be) is the kernel times out, the raid handles the
> read error by trying a rewrite, the drive is still hung on the read
> error so it doesn't respond to the write request, and the drive gets
> kicked for a write failure.

Oh yes you are correct, so the drive would be kicked after 60secs and 
not after 30secs contrary to what I said.
So the sequence would be: drive stuck on read --> scsi read failure due 
to timeout at the 30th second --> MD receives failure and attempts 
rewrite --> scsi write failure due to timeout at the 60th second --> 
drive kicked by MD at the 60th second
I think this is what should have happened, but it didn't happen like 
this anyway so I think there is probably a kernel bug somewhere.