Re: Replacing disk in Linux Software RAID 1

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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@xxxxxxxxxxxxxxx>
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@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.


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



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