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Old 09-22-2005, 01:38 PM   #1
khooke
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Adding additional drive to make a RAID 1 config


I have an IDE RAID controller card (SiL 680) in my server and 1 40GB drive, and currently no RAID config. The machine is running Fedora Core 4.

If I add an additional identical hard drive and set up a RAID 1 configuration in the BIOS settings, mirroring the existing drive to the other, what are the implications for the existing linux install on this machine?

As the config is controlled by the hardware card will there be any additional config needed for linux to work with this arrangement, and is this a good idea (rather than doing a fresh install?)

Thanks!

Last edited by khooke; 09-22-2005 at 01:55 PM.
 
Old 09-23-2005, 11:04 AM   #2
MensaWater
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From my very limited experience on Linux RAID stuff I'd say probably best to reinstall especially if you're changing it at the firmware leve.

My reasoning is that you layout the filesystem on the raid devices. In the Linux HW raid I've seen the device is actually seen as if it were one drive so it suggests the device you have now would go away in favor of the "new" one presented by the firmware. If they are both /dev/hda then it seems likely you'd have an issue.

On the Software RAID which I've seen it actually uses the existing devices and creates a metadevice so it MIGHT work but here again since one mounts the meta device I suspect it lays out the filesystem on top of that.

Notes I wrote myself a couple of weeks ago on the software RAID:

Did research on /dev/md* devices seen on server. These are software
RAID1 (mirror) devices. fdisk doesn't work on them. Found info that
indicates they are described in /etc/raidtab. Man pages regarding
mkraid, raidstart & raidstop exist. Also found good post talking about
this:
http://www.linuxquestions.org/questi...hreadid=352756
Original question there talks about mdadm but no such command here.
Maybe it is something in newer versions of the raid stuff but it doesn't
seem necessary based on my read of the post and the man pages.

The raidtab on above system contains:
raiddev /dev/md3
raid-level 1
nr-raid-disks 2
chunk-size 64k
persistent-superblock 1
nr-spare-disks 0
device /dev/sda5
raid-disk 0
device /dev/sdb5
raid-disk 1
raiddev /dev/md0
raid-level 1
nr-raid-disks 2
chunk-size 64k
persistent-superblock 1
nr-spare-disks 0
device /dev/sda1
raid-disk 0
device /dev/sdb1
raid-disk 1
raiddev /dev/md2
raid-level 1
nr-raid-disks 2
chunk-size 64k
persistent-superblock 1
nr-spare-disks 0
device /dev/sda3
raid-disk 0
device /dev/sdb3
raid-disk 1
raiddev /dev/md1
raid-level 1
nr-raid-disks 2
chunk-size 64k
persistent-superblock 1
nr-spare-disks 0
device /dev/sda2
raid-disk 0
device /dev/sdb2
raid-disk 1

On HP-UX systems we use MirrorDisk/UX which does allow us to add a second drive after the initial install but as stated I don't think it works that way on Linux. Since you're considering reloading anyway you might want to go ahead and take a backup then try it without reload - if it doesn't work you can then do the reload then restore the backup.
 
Old 09-25-2005, 01:39 AM   #3
khooke
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Registered: Sep 2005
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Ok, thanks for the advice. If I go ahead and do it I'll try to reinstall onto the new RAID config.

Thanks,Kevin
 
  


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