[ale] new to raiding

[Denny Chambers]

Cade Thacker wrote:
> 
> Hi Ho,
> 
> I have mirrored two 1 gig drives at /home and my wife, via samba, is
> saving her Grad school papers onto that share.
> 
> So my question is,
> 
> 1) how bomb proof is that mirroring.

Well the Titanic is not unsinkable, but you should be pretty safe. If
you want addition protection, look into adding a journeling file system
like xfs, ext3, or rieserfs. Do regular backups!! Just because you
mirror the drive doesn't mean you should not back it up as well. Make
sure your mirrored drives are on different ide controllers, so that loss
of a ribbon cable or ide channel doesn't take both drives down. 
> 
> 2) should a drive go down what happens.
>From a user perspective nothing. Your not talking to the hard drives
anymore. Your talking to a single abstract device (md0, md1, etc). The
abstract device is talking to your two drives. So even if you lose a
hard drive, as a user all you know about is this md device that your
talking to. As long as 1 hard drive is working the md device will keep
working.  You will need to monitor the raid device from time to time
(cat /proc/mdstat) to make sure that the raid is still happy, and watch
you syslog files.
> 
> 3) how do I replace a drive, will it automagically pick it up, and bring
> it up to speed?
No, not that I recall. I think you will need to manually create a
partition on the drive that is the same size or larger than the
partition that you are trying to mirror, then you will need to do
raidhotadd of the partition back into the raid set. Then the mirror will
sink back up.  
> 
> 4) Can I boot with a mirrored drive unplugged?
Sure! Just as long as your boot partition is not on the unplugged drive.
The md device will just come up in a de-graded mode, which for a mirror
is not very de-graded as far as performance is goes (No more overhead
having to write to two drives), but you will not have you mirrored
protection.

hope this helps,
Denny
> 
> Thanks in advance.
> 
> --cade
> 
> ==========
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> =========
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-- 
Denny Chambers
Quantum Corporation
Storage Solutions Group
Senior Software Engineer

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