[CentOS] raid1 creation :: not large enough to join array

[Ross Walker]

On Jan 16, 2010, at 11:46 AM, Les Mikesell <lesmikesell at gmail.com>  
wrote:

> Adrian Sevcenco wrote:
>> Ross Walker wrote:
>>> On Jan 16, 2010, at 10:27 AM, Adrian Sevcenco
>>> <Adrian.Sevcenco at cern.ch> wrote:
>>>
>>>> Hi!
>>>> I have 2 identical hdd (1002FBYS) with the same firmware, etc ..
>>>> really
>>>> identical! when i try to add the second hdd to this raid1 array i  
>>>> have
>>>> the message that /dev/sdb is not large enough to join array!!
>>>> on the first hdd i have 100 mb unpartitioned at the end of disk  
>>>> (as i
>>>> understood that mdadm put there some info...)
>>>> Anyone, any idea what can be wrong? i already done this procees
>>>> several
>>>> times and this is first time i encounter this and i have no idea  
>>>> what
>>>> can be the problem ..
>>> Make sure the partitions are exactly the same, you can use sfdisk to
>>> copy the table from a to b.
>> well, i was doing raid over device (md_dX) but i found out the  
>> problem :
>> even if there are "identical" devices, they have different number of
>> blocks (hdparm output). how is this possible?
>> is there a way to restrict the number of blocks that a hdd have?
>> alternative would be just to clone the first hdd on the "smaller" one
>> and then add the big one to and raid1 array ...
>>
>> Did someone seen this situation?
>
> I've seen a case where single drive volumes initialized in different  
> (but
> identical) IBM 3550's with adaptec raid controlers would end up with  
> slightly
> different sizes and wouldn't match up if moved.  I think this was a  
> bios or
> firmware difference but I'm not exactly sure.  I was trying to clone  
> disks and
> just started over with the smaller source so it would work everywhere.

Les might be on to something here I remember some BIOS store a per- 
device LBA setting which might cause to sizes to differ.

This brings up a good reason to use partitions as it will allow you to  
coerce the size down a little 128-256MB so if you need to replace a  
drive with a different manufacturer's drive in the future you will  
have a better chance in making it fit.

-Ross