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sirlark
Guru
Joined: 25 Oct 2004
Posts: 306
Location: Limerick, Ireland
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 Posted: Wed May 04, 2011 10:08 am Post subject: How safe is it to use mdadm to hot add to rootfs raid |
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I have a two identical hdds in a home server machine. They are each partitioned identically: boot, root, swap. On initial install, I set up the root partition as a mirror RAID over /dev/sda2 (root) and /dev/sdb2 (root), boot is /dev/sda1, and swap is /dev/sda3. I then added an extra drive for backup storage, and my drives got renamed. The new drive became /dev/sda. I have changed grub to point to /dev/sdb1 for the boot partition and the fstab uses /dev/sdb3 for swap.
| Code: | | mdadm --detail /dev/md0 |
tells me that the RAID has only one active drive now. My question is simply if it's safe to to hot add the old /dev/sdb2 (not /dev/sdc2) to the RAID, specifically will the newly added drive be overwritten with the current contents, or is it possible that the newly added drive, being originally a drive in the array, would somehow cause the RAID to synchronize to the stale data on /dev/sdc2 (the newly added drive)
The command I'm thinking of running is
| Code: | | mdadm -A /dev/md0 -a /dev/sdc2 |
Thanks
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frostschutz
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Joined: 22 Feb 2005
Posts: 2977
Location: Germany
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| Posted: Wed May 04, 2011 10:23 am Post subject: |
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mdadm is perfectly safe, just as dd is perfectly safe, unless of course you don't understand what will happen and you end up using it wrong, like holding a gun the wrong way and shooting yourself
Look at /proc/mdstat
It tells you which drive is currently in use. If you add a new drive, it will sync from the currently active drive, to the newly added drive, thus the contents on the added drive will be overwritten by the sync. |
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