Hello,
I would like to replace one of the disks in a raid 1 array (software raid)
in centos 4.4 for the purpose of >saving the removed drive as a backup of
the system. Replace it with a new disk and have the raod >resync. That
way the removed disk can be used to restore the system to that point in
time if something >dramatic occured.
I have a number of questions, I can’t find the answers to and I don't have
a system I can play with to see >how the software behaves:
1) Do I need to partition the replacement drive or will the system do it
after reboot?
2) Should I break the raid before replacement or just shutdown, replace and
reboot?
3) I have also read that acronis 10 rescue CD can be booted and take a
system image that way but I >have not tried that yet..
In general, are these approaches a good idea for generating an offsite
image backup??
Any help or input would be appreciated.
Thank you,
-ed-
Hello, Ed.
We will most probably have to talk together. I have the exact same purpose
than you have. I am working like this since several years and it is
absolutely great (with mdadm software raid 1).
I do even go further: I synchronise remotely a complete system on a local
software raid system with rsync and then I can boot up the backuped system
whenever I want, and it will just be a working and bootable backup mirror,
on another system. But it is not always so easy, problems do arise doing
this, and I am working on it.
To answer your questions:
1) You need to fdisk your partitions yourself on the disk, exactly the same
way the source partitions have been done, it is not done automatically. Once
this is done, you need to add the partitions to the working md array. It
takes time to synchronise everything. All depends on the speed of your disk
transfer, but if you have about 50Mbytes/sec, you need more than a hour for
a 200 Gbytes array.
2) You don't need to break the raid (I suppose mark the disk to be removed
as failed and then remove it from the array), before shutting down. You can
simply shutdown the system, remove and replace the disk, and then the system
will start up with only one drive out of two (of course supposing that you
use raid 1, mirroring).
However, warning: you need to have the boot loader installed on the disk
which will remain on the system. If this is not the case, there will be no
reboot at all !
Also, if you are using the boot partion also as raid1 device, you will come
into troubles, because it won't find theboot partition to boot from. This is
due to the fact that you define the proper boot partition disk in the
/boot/grub/devices.map file. This device is different for each drive array,
and thus it won't work out of the box. Therefore, the proper way to work is
to have the boot partition not as raid device, but the second partition must
be a normal ext3 partition, and must be a copy of everything, except the
/boot/grub/device.map file.
3) No idea, but you should be able to do it through the CentOS 4.4 Live CD
also.
Regards,
Daniel
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