Replacing disk in Linux Software RAID 1

[Robin Laing]

Michael E. Webster wrote:
> Michael,
> 
> Probably - I went with "ghost" because I had a boot floppy handy.
> 
> The main thing is to get the MBR from that first drive - without it,
> you're out of luck.  
> 
> In software RAID, the MBR is only written to the first drive, which
> really doesn't make sense.  I would think that if you had the first
> drive fail, you should be able to boot off the second one - IMHO.
> 
> 
> Mike.
> 
> 
> 
> On Fri, 2004-08-13 at 18:10, Michael Mansour wrote:
> 
>>Hi Michael,
>>
>>Many thanks for the below, I'll try this process
>>tonight.
>>
>>With the "Ghost", could I simply boot from a Live
>>Rescue CD and use something like:
>>
>># dd if=/dev/hdg of=/dev/hde
>>
>>where /dev/hde would be the new blank drive?
>>
>>Michael.
>>
>> --- "Michael E. Webster" <mwebster at intercosmos.com>
>>wrote: 
>>
>>>Michael, 
>>>
>>>Whaddaya know..  I just happen to have a recipe for
>>>doing this.
>>>I went through a similar problem about two months
>>>ago.
>>>Just substitute /dev/hde and /def/hdg where
>>>applicable.
>>>
>>>
>>>Copy the MBR to /dev/hdc (done before procedure)
>>>
>>>prompt# grub
>>>
>>>Grub> device (hd0) /dev/hdc
>>>
>>>Grub> root (hd0,0)
>>>
>>>Grub> setup (hd0)
>>>
>>>
>>>Make sure that we have the partition table for all
>>>drives backed up
>>>(done before)
>>>
>>>prompt# sfdisk -d /dev/hda >
>>>/raidinfo/partitions.hda
>>>
>>>prompt# sfdisk -d /dev/hdc >
>>>/raidinfo/partitions.hdc
>>>
>>>prompt# more /proc/mdstat > /raidinfo/mdstat.md
>>>
>>>
>>>Estimated time: zero minutes
>>>
>>>
>>>Shutdown the box
>>>
>>>Remove /dev/hda and label as â??hda badâ??
>>>
>>>Boot box to make sure it boots
>>>
>>>Shutdown server and place new blank drive in ide0
>>>(new hda)
>>>
>>>Estimated time: ten minutes 
>>>
>>>
>>>Ghost ide1 (hdc) to ide0 (hda)
>>>
>>>Do â??Boot Imageâ?? copy
>>>
>>>Estimated time: a little more than an hour
>>>
>>>
>>>Remove ide1 (original hdc) and label as â??hdc
>>>goodâ??
>>>
>>>Power on to make sure ide0 (new hda) boots
>>>
>>>Shutdown and place new blank drive in ide1 (new hdc)
>>>
>>>Power on to make sure it boots
>>>
>>>Shutdown
>>>
>>>Estimated time: fifteen minutes
>>>
>>>
>>>Power on and boot
>>>
>>>Copy the MBR to hdc
>>>
>>>prompt# grub
>>>
>>>Grub> device (hd0) /dev/hda
>>>
>>>Grub> root (hd0,0)
>>>
>>>
>>>
>>>Hope this helps,
>>>Mike.
>>>
>>>
>>>
>>>
>>>On Fri, 2004-08-13 at 17:51, Michael Mansour wrote:
>>>
>>>>Hi,
>>>>
>>>>I have a server with a 2 disk Linux Software RAID
>>>
>>>1
>>>
>>>>setup (two 80Gb disks). The first device is
>>>
>>>/dev/hde
>>>
>>>>and the second is /dev/hdg.
>>>>
>>>>The /dev/hde device is ready to fail, as it
>>>
>>>produces
>>>
>>>>various SMART errors using smartctl and fails on a
>>>>self-test with:
>>>>
>>>>[root at gazelle root]# smartctl -l selftest /dev/hde
>>>>smartctl version 5.30 Copyright (C) 2002-4 Bruce
>>>
>>>Allen
>>>
>>>>Home page is http://smartmontools.sourceforge.net/
>>>>
>>>>=== START OF READ SMART DATA SECTION ===
>>>>SMART Self-test log structure revision number 1
>>>>Num  Test_Description    Status                 
>>>>Remaining  LifeTime(hours)  LBA_of_first_error
>>>># 1  Short offline       Completed: read failure  
>>>
>>>   
>>>
>>>>90%        34         0x0463c0ee
>>>># 2  Short offline       Completed: read failure  
>>>
>>>   
>>>
>>>>90%      1087         0x0425290c
>>>># 3  Extended offline    Completed: read failure  
>>>
>>>   
>>>
>>>>90%      1072         0x0425290c
>>>># 4  Short offline       Completed: read failure  
>>>
>>>   
>>>
>>>>90%      1072         0x0425290c
>>>># 5  Short offline       Completed: read failure  
>>>
>>>   
>>>
>>>>90%      1071         0x0425290c
>>>>
>>>>The server is running Fedora Core 1.
>>>>
>>>>I have the new 80Gb disk and wish to replace
>>>
>>>/dev/hde
>>>
>>>>device with the new disk, how do I do this?
>>>>
>>>>The following is how I have the mirror setup:
>>>>
>>>># fdisk -l /dev/hde
>>>>
>>>>Disk /dev/hde: 80.0 GB, 80026361856 bytes
>>>>255 heads, 63 sectors/track, 9729 cylinders
>>>>Units = cylinders of 16065 * 512 = 8225280 bytes
>>>>
>>>>   Device Boot    Start       End    Blocks   Id 
>>>>System
>>>>/dev/hde1   *         1       395   3172806    b 
>>>>Win95 FAT32
>>>>/dev/hde2           396       408    104422+  fd 
>>>>Linux raid autodetect
>>>>/dev/hde3           409      1070   5317515   fd 
>>>>Linux raid autodetect
>>>>/dev/hde4          1071      9729  69553417+   f 
>>>>Win95 Ext'd (LBA)
>>>>/dev/hde5          1071      1331   2096451   fd 
>>>>Linux raid autodetect
>>>>/dev/hde6          1332      1585   2040223+  fd 
>>>>Linux raid autodetect
>>>>/dev/hde7          1586      1716   1052226   fd 
>>>>Linux raid autodetect
>>>>/dev/hde8          1717      4327  20972826   fd 
>>>>Linux raid autodetect
>>>>/dev/hde9          4328      9729  43391533+  fd 
>>>>Linux raid autodetect
>>>>
>>>>with /dev/hdg being exactly like above.
>>>>
>>>>As soon as I pull out the /dev/hde device, the
>>>
>>>server
>>>
>>>>won't boot (as grub only resides on /dev/hde), so
>>>
>>>I
>>>
>>>>also installed grub on /dev/hdg to overcome that
>>>>problem. But now I'm wondering what I must do to
>>>
>>>pull
>>>
>>>>out /dev/hde and replace it with the new drive
>>>
>>>(which
>>>
>>>>doesn't have any partitioning setup) and then
>>>
>>>force
>>>
>>>>Linux to resync the data on /dev/hdg to the new
>>>>/dev/hde?
>>>>
>>>>Is there some way I have to fail the /dev/hde
>>>
>>>drive,
>>>
>>>>replace it then put it back on-line? First time
>>>
>>>I've
>>>
>>>>done this with Software RAID so I'm not sure.
>>>>
>>>>Any advice is appreciated.
>>>>
>>>>Michael.
>>>>
>>>>
>>>>Find local movie times and trailers on Yahoo!
>>>
>>>Movies.
>>>
>>>>http://au.movies.yahoo.com
>>>>
>>>
>>>
>>>-- 
>>>fedora-list mailing list
>>>fedora-list at redhat.com
>>>To unsubscribe:
>>>http://www.redhat.com/mailman/listinfo/fedora-list
>>>
>>
>>=== message truncated === 
>>
>>Find local movie times and trailers on Yahoo! Movies.
>>http://au.movies.yahoo.com
>>
> 
> 
> 

Would it be possible to write the MBR to the second disk just in case?
-- 
Robin Laing