[gentoo-user] Recovering RAID1 after disk failure

[gentoo-user] Recovering RAID1 after disk failure

[Mike Diehl]

Hi all,

I've got a sw RAID1 that just had a failed drive replaced with an identical 
drive.

However, the good drive started on sector 63 and the new drive want's to start 
on sector 2048.  Fdisk won't let me create the partition table on the new 
drive as it is on the old drive.

This is the good drive in the RAID:
===============================================
Disk /dev/sdb: 320.1 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders, total 625142448 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xfc32270f

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1              63      224909      112423+  fd  Linux raid autodetect
/dev/sdb2          224910    50572619    25173855   82  Linux swap / Solaris
/dev/sdb3        50572620   625137344   287282362+  fd  Linux raid autodetect
===============================================

However, after zero'ing out the new drive, this is what fdisk allows me to do:


===============================================
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF 
disklabel
Building a new DOS disklabel with disk identifier 0xfcd585e4.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4, default 1): 1
First sector (2048-625142447, default 2048):
===============================================

As you can see, I can't mirror the previous partitioning scheme and I will 
probably not have enough space on the new drive to build the RAID!

What can I do?



-- 

Take care and have fun,
Mike Diehl.

Re: [gentoo-user] Recovering RAID1 after disk failure

[Paul Hartman]

On Thu, Jun 16, 2011 at 10:00 PM, Mike Diehl <mdiehl@diehlnet.com> wrote:
> I've got a sw RAID1 that just had a failed drive replaced with an identical
> drive.
>
> However, the good drive started on sector 63 and the new drive want's to start
> on sector 2048.  Fdisk won't let me create the partition table on the new
> drive as it is on the old drive.

Hi Mike,

I believe this is due to the alignment code in newer versions of fdisk
(2048 sector = 1 megabyte)

I think you can use the expert menu in fdisk ("x" from the main menu)
to achieve what you're trying to do. I can't tell you the exact steps
but I am 99.9% sure it can be done.

Re: [gentoo-user] Recovering RAID1 after disk failure

[Mike Diehl]

Looks like I can take it from here!  Thank you.  I didn't know fdisk had an 
"expert" menu.... <wink>

On Thursday 16 June 2011 11:14:30 pm Paul Hartman wrote:
> On Thu, Jun 16, 2011 at 10:00 PM, Mike Diehl <mdiehl@diehlnet.com> wrote:
> > I've got a sw RAID1 that just had a failed drive replaced with an
> > identical drive.
> > 
> > However, the good drive started on sector 63 and the new drive want's to
> > start on sector 2048.  Fdisk won't let me create the partition table on
> > the new drive as it is on the old drive.
> 
> Hi Mike,
> 
> I believe this is due to the alignment code in newer versions of fdisk
> (2048 sector = 1 megabyte)
> 
> I think you can use the expert menu in fdisk ("x" from the main menu)
> to achieve what you're trying to do. I can't tell you the exact steps
> but I am 99.9% sure it can be done.

-- 

Take care and have fun,
Mike Diehl.

Re: [gentoo-user] Recovering RAID1 after disk failure

[Andrea Conti]

Hello,

> However, the good drive started on sector 63 and the new drive want's to start 
> on sector 2048.  Fdisk won't let me create the partition table on the new 
> drive as it is on the old drive.

Recent versions of fdisk require partitions to begin on a 1MB boundary;
this among other things guarantees that there are no alignment issues
with 4k-sector drives.

If you really need to use fdisk for this task you can start it in
compatibility mode (i.e. "fdisk -c=dos").

The recommended way of preparing the new drive, though, is to simply use
sfdisk to copy the partition table from the existing one:

sfdisk -d <old drive> | sfdisk -L <new drive>

andrea

Re: [gentoo-user] Recovering RAID1 after disk failure

[Mike Diehl]

I've got my drive partitioned, but I WILL read up on sfdisk.  Thanks for the 
pointer.

On Friday 17 June 2011 12:27:15 am Andrea Conti wrote:
> Hello,
> 
> > However, the good drive started on sector 63 and the new drive want's to
> > start on sector 2048.  Fdisk won't let me create the partition table on
> > the new drive as it is on the old drive.
> 
> Recent versions of fdisk require partitions to begin on a 1MB boundary;
> this among other things guarantees that there are no alignment issues
> with 4k-sector drives.
> 
> If you really need to use fdisk for this task you can start it in
> compatibility mode (i.e. "fdisk -c=dos").
> 
> The recommended way of preparing the new drive, though, is to simply use
> sfdisk to copy the partition table from the existing one:
> 
> sfdisk -d <old drive> | sfdisk -L <new drive>
> 
> andrea

-- 

Take care and have fun,
Mike Diehl.