Re: trying to understand assemble option in mdadm please help.
On Mon, Jul 16, 2012 at 6:39 PM, Gary Dale <garydale@rogers.com> wrote:
> On 16/07/12 08:12 AM, Muhammad Yousuf Khan wrote:
>>
>> apart from my question i know what does "assemble" mean but most of
>> the time it create conflict with the option "add".
>> for example.
>>
>> if raid is broken then i can just re-add the the broken partition
>>
>> if my HD fails then i will add the new drive, recreate the partition
>> and add it to new array and cat /proc/mdstat will show me the sync
>> status.
>>
>> but now the next question coming in my mind is why assemble.
>>
>> i also observed that some time when i restart the computer contain
>> RAID1 after 2 or 3 months it start to test or (maybe)assemble one of
>> the partition by saying that (more or less) that the raid has not been
>> tested for this this days so now reassembling (sorry if i am wrong
>> since i can not recall the whole message)
>> so the point why assemble is necessary?
>>
>> if assembling is that necessary then why should i wait to restart. i
>> can do this manually every week or can schedule a task for it.
>>
>> Thanks,
>
> Assemble builds the arrays based on the information contained in the
> superblock. The testing you are talking about is more likely fsck checking
> the file system(s) on the arrays.
if Assemble builds the array then what is the purpose of "--create"
option. sorry if my question is a bit annoying but i am confuse in
this.
is there a difference in creating and building the array?
Thanks,
>
> It is possible for arrays to get out of sync due to a power outage or
> improper shutdown but in practice this is unlikely. Nonetheless, mdadm
> should also check for the consistency of the arrays periodically. If it
> doesn't do this and a drive fails, it may not be possible to rebuild the
> array.
>
> The /etc/crontab.d folder on my Wheezy system contains an mdadm entry which
> was put there by the package maintainer or developer. It includes the line:
>
> 57 0 * * 0 root if [ -x /usr/share/mdadm/checkarray ] && [ $(date +\%d) -le
> 7 ]; then /usr/share/mdadm/checkarray --cron --all --idle --quiet; fi
>
> which checks all the arrays once a month. This is a trade off since you
> don't want to spend too much time checking arrays. If possible, you may want
> to run checkarray before your drive has failed to ensure that your array is
> consistent before pulling the failing drive.
>
>
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