Re: Linux raid wiki

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

On 26/09/16 15:01, Phil Turmel wrote:
> Hi Wol,
> 
> A few comments below.

Thank you very much.
> 
> On 09/24/2016 09:18 AM, Wols Lists wrote:
>> On 23/09/16 00:31, Wols Lists wrote:
>>> I've added the "When Things Go Wrogn" section, but so far only the first
>>> two pages - "Asking for help" and "Timeout Mismatch" - are all my work.
>>> The other three pages were already there, but I moved them here because
>>> I felt they belonged here.
>>>
>>> Please feel free to criticize it (or offer bouquets :-), and give advice
>>> as how to improve things, either in private email or on the list.
>>
>> Replying to myself, but I'm reasonably happy with the first three
>> sections in "When Things Go Wrogn". But it's important that they're
>> correct! Would a couple of experts mind looking them over and sending a
>> critique to the list? Just a simple "Looks good" would be great and set
>> my mind at rest that I have understood things properly and I'm not
>> giving out bad advice.
>>
>> Note that the next section is going to be along the lines of "My array
>> won't assemble / run"
>>
>> https://raid.wiki.kernel.org/index.php/Asking_for_help
> 
> "smartctl --all" doesn't report ERC settings.  --xall is required, or
> for a somewhat shorter report, I find "smartctl -H -i -l scterc" ideal.
> 
Thanks. Noted and updated.

>> https://raid.wiki.kernel.org/index.php/Timeout_Mismatch
> 
> Very good.
> 
>> https://raid.wiki.kernel.org/index.php/Replacing_a_failed_drive
> 
> You should note that USB connections are not suitable for permanent use.
>  Copying a drive or doing a --replace, fine, but don't leave it set up
> that way.  USB disconnects, even if only for sleep, will scramble the MD
> code.

Noted. I've added a bit to say don't use USB for raid but it's okay for
salvaging a drive.
> 
> Also, any time ddrescue is used, the unreadable sectors are replaced
> with zeros and there is no longer any indication that that sector is
> bad.  That means assembling an array from ddrescued components will
> certainly have some corrupt spots.  fsck is mandatory, and there may be
> corrupt file content.  ddrescue is only appropriate if there's no
> redundancy left in the array to use to fix UREs.
> 
Or if there are no errors in the copy ...

That section tries to stress that it only applies if there are no
errors. And if you complete it successfully, you won't lose any data.

> Overall, very good.
> 
The next section -

https://raid.wiki.kernel.org/index.php/Assemble_Run

addresses what to do if the array is messed up in some way. Would you
mind taking a look at that now too :-)

Cheers,
Wol