Re: Disk Monitoring

[Wols Lists <antlists@youngman.org.uk>]

On 29/06/17 11:16, Gandalf Corvotempesta wrote:
> 2017-06-29 12:14 GMT+02:00 Mateusz Korniak <mateusz-lists@ant.gliwice.pl>:
>> One can read of all disks/partitions used by RAIDs by script
>> /usr/share/mdadm/checkarray
>>
>> In many distros it is set to be performed monthly out-of-box.
> 
> I know this and I'm running weekly. (just to be sure)
> What Is unclear to me is why an hardware raid controller like LSI, has
> two different kind of checks: patrol read and consistency check.

Because they're two completely different things.

A patrol check reads the entire disk. It doesn't give two hoots what the
data is, it just cares that the data can actually be retrieved from the
disk.

A consistency check, on the other hand, wants to make sure that the data
is correct. It will read both copies of a mirror and compare them. Or it
will read the data from 4/5/6, calculate the parities, then read them
from disk and compare them.

In other words, a patrol check looks for a failing disk. A consistency
check looks for corrupt data. (A consistency check does a patrol check
as a side effect, but you might not want to do just that, as it is
computationally much more expensive. You might want to do a patrol check
every day, and a consistency check of a weekend.)

Cheers,
Wol