Greg Oster wrote:
> Mark Cullen writes:
> 
>>Greg Oster wrote:
>>
>>>Mark Cullen writes:
> 
> [snip]
> 
>>>
>>>If the array won't be used again, then just make sure you do a 
>>>'raidctl -A no raid0' so that the components don't get auto-configured.
>>>You can then do a 'raidctl -u raid0' to unconfigure.  If you want to 
>>>nuke the labels (something that raidctl doesn't have an option for)
>>>you can use something like:  
>>>
>>> dd if=/dev/zero of=/dev/wd1a bs=512 count=1 seek=32
>>
>>You mean, if I just do a `raidctl -u raid0`, if I were to reboot the 
>>array would infact reappear and 'auto-configure' itself?
> 
> 
> If you had done a 'raidctl -A yes raid0', then "yes".  Doing an 
> unconfigure doesn't change the autoconfigure status.
> 

Yeah, I did a `raidctl -A yes raid0`. Quite neat then :-)

> 
>>Under what situation(s) might I want to nuke the labels? A little 
>>confused there :)
> 
> 
> E.g. if you planned to move the disk to a different machine, and add 
> it to a different array...  

Ah! I see, thanks!

>  
> 
>>>>Suprisingly, even though the data on these two disks now differs, the 
>>>>status of the array is ok on both disks. I assume this is because I 
>>>>forced a reconfiguration, and there's really no easy way to tell that 
>>>>the data differs.
>>>
>>>
>>>Yes...  "-C" is to be used for new arrays with nothing on them, or
>>>when you want to say "I know better, trust me"...  
>>
>>So, this would indeed be the correct way of taking a disk (not a spare) 
>>out of the array configuration, as I have in the examples?
> 
> 
> Using '-c' would be better, as that would at least make sure that the 
> remaining components are at least consistent with each other.  ('-C' 
> overrides any consistency checks..)

I do seem to recall trying -c, but it didn't seem to like it. I'll try 
again later and get the error if this is strange news?

> 
> 
>>>
>>>>A `raidctl -i raid0` succeeds (admittedly I have no 
>>>>idea what it does, however),
>>>
>>>
>>>For a RAID 1 configuration, it will verify the that the data bits 
>>>are in sync... 
>>
>>Now this is interesting... see below
>>
>>
>>>
>>>>but the data on the two disks is still 
>>>>different, that is, /dev/wd3a still has the old copy of the data. 
>>>
>>>
>>>Um... after the 'raidctl -i raid0' completes, the data parts of wd1a 
>>>and wd3a had better be *exactly* the same!
>>
>>They weren't the same afterwards! If I mounted just the disk that was 
>>missing when I added the new data, after doing an -i, the data was *not* 
>>there on that disk. I had to force a rebuild of the disk in order to get 
>>the data on to it.
>>
>>However, I may know why? I took wd1 out, and put the new data on wd3. If 
>>I issue a -i, does it use the first disk in the array config to rebuild 
>>the parity? 
> 
> 
> Yes.  The first disk in a RAID 1 set is considered the 'master', and 
> in the face of having 2 disks where it can't tell which is "more 
> correct", the 'master' will be used as the difinitive source.
> 
> 
>>This would have meant the old copy of data on wd1 would have 
>>been used?!
> 
> 
> Yes.  So what you would have seen on wd3 should have been the old 
> data. (and the new data that was on wd3 would be gone).
> 
> The data bits *have* to be the same after a '-i'.  If they arn't then 
> I've got a pretty serious bug to fix...


I'll rerun the 'simulation' and check this one out. I never thought to 
check whether the data on wd3 got obliterated in the process or not :-)

> 
> 
>>>
>>>>In 
>>>>such a situation then, am I to force the re-added disk to "failed" and 
>>>>rebuild it?
>>>
>>>
>>>Yes.  With raid0 in operation with just wd1a, you could have done:
>>>
>>> raidctl -a /dev/wd3a raid0
>>> raidctl -vF absent raid0
>>>
>>>and watched it rebuild :)
>>
>>Ah! Would that have put /dev/wd3a in to the 'absent' slot, and removed 
>>it from the 'spares'? If so, that's quite neat!!
> 
> 
> It's not *quite* that automated yet, but with a quick reboot it would 
> automatically move to the right spot... 

Quite cool! I did actually do an `raidctl -a /dev/wdXa raid0` with an 
absent disk, and it got put in the 'spares'. I tried to do a `raidctl -r 
/dev/wdXa raid0`, but it didn't actually get removed from the spares. It 
seemed to do nothing at all from what I remember. I'll have to check 
that one again too, as I am sure that's probably not normal.

> 
> 
>>Thanks for your reply Greg :)
> 
> 
> No problem :)
> 
> Later...
> 
> Greg Oster
> 
> 
>