Re: mdadm --monitor: need extra feature?

[NeilBrown <neilb@suse.de>]

[-- Attachment #1: Type: text/plain, Size: 2647 bytes --]

On Wed, 22 Aug 2012 09:14:15 +0200 Sergiusz Brzeziński
<Sergiusz.Brzezinski@supersystem.pl> wrote:

> W dniu 21.08.2012 14:39, Adam Goryachev pisze:
> > On 21/08/12 21:51, Sergiusz Brzeziński wrote:
> >>
> >>
> >> W dniu 21.08.2012 12:44, David Brown pisze:
> >>> On 21/08/2012 12:41, Sergiusz Brzeziński wrote:
> >>>> Hi,
> >>>>
> >>>> I use Raid1 to make backup of the whole system.
> >>>
> >>> Raid is not a backup system. It is to improve uptimes, minimise
> >>> downtimes due to
> >>> disk failures, and possibly to improve disk speed and/or capacity.
> >>>
> >>> I would recommend you first think about what you are trying to
> >>> achieve here -
> >>> what are you trying to back up, how do you see restores being used, how
> >>> efficiently are you using your hardware, your bandwidth, your time
> >>> and effort?
> >>>
> >>> You would probably be better off with a normal fixed 2-disk raid1 to
> >>> minimise
> >>> the problems caused by a single disk failure, combined with an rsync
> >>> snapshot
> >>> style backup that can be fully automated and give quick and easy
> >>> recovery of
> >>> multiple old versions of files in the face of the most common cause
> >>> of data loss
> >>> - human error.
> >> [...]
> >>
> >> I know, I know. Raid is not a backup system :)
> > Aside from RAID is not a backup, perhaps the more useful suggestion
> > would be to use the right tool for the job...
> >
> > So, again, ignoring that you possibly should not be using RAID for a
> > backup... how about using udev scripts to see when you plugin a drive,
> > and that script can check the UUID against any md arrays, and if it
> > matches, add it to the array....
> 
> I wrote a script making this work. It runs once a hour. I pass the parameter 
> with md device to the script. It checks the state of the array with "mdadm 
> --detail". If there is something wrong (State : degraded) it reads UUID of that 
> array. Then it scans for /dev/sd* partitions and checks with "mdadm --examine" 
> if UUID matches. If so, the partition can be added with "mdadm --add". That is 
> why I asked abut this feature in mdadm - recognising if there is a new partition 
> belonging to monitored array. With mdadm this procedure would work on elegant 
> manner.
>

udev really is the right way to do this.  Just get udev to run
  mdadm -I /dev/newdev
whenever a device is discovered.  It can then be automatically re-added
depending on the policy set up in mdadm.conf.
"mdadm --monitor" will not gain this functionality.  It is for monitoring
active arrays, not for monitor new devices.

NeilBrown


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 828 bytes --]