Re: trying to understand assemble option in mdadm please help.
or just one thing if you please explain these commands. i think my
confusion will be cleared
mdadm --assemble /dev/md1 /dev/hda1
mdadm --assemble /dev/md3 /dev/hda3
mdadm --add /dev/md1 /dev/hdb1
mdadm --add /dev/md3 /dev/hdb3
what is the difference in both command thanks. any help will be highly
appreciated.
On Wed, Jul 18, 2012 at 12:36 AM, Muhammad Yousuf Khan <sirtcp@gmail.com> wrote:
> 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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