[CentOS] Software RAID Level 1, smartd and changing dev numbers

Wed Feb 16 18:46:54 UTC 2011
Keith Roberts <keith at karsites.net>

On Wed, 16 Feb 2011, James Smallacombe wrote:

> To: CentOS mailing list <centos at centos.org>
> From: James Smallacombe <james at sicom.com>
> Subject: Re: [CentOS] Software RAID Level 1, smartd and changing dev numbers
>> At Wed, 16 Feb 2011 12:00:27 -0500 (EST) CentOS mailing list
>> <centos at centos.org> wrote:
>>> The problem is, the kernel seemingly randomly switches 
>>> between /dev/sdb and /dev/sdc for these devices.  This 
>>> makes the process slower by requiring more manual input 
>>> where a script(s) could otherwise suffice.
>> I'm assuming these are actually SATA disks with a 
>> controller that supports hot-swap.
> Correct.
>> What I think is happening is that the kernel retains some 'memory' of
>> the pulled drive (say /dev/sdb) and when the fresh drive is installed, a
>> new dev file is created (/dev/sdc).  Eventually, /dev/sdb is forgotten
>> by the time the next 'swap' and /dev/sdb is assigned to the next fresh
>> disk.
> Interesting...one would think that this behavior would be consistent
> across all servers then, but it isn't.  Most accept the same dev,
> /dev/sdb, but some assign /dev/sdc.  Is there a way to just disable
> /dev/sdc and force the kernel to use /dev/sdb every time?

Can you identify any differences in the machines that don't 
re-assign the dev files, and the machines that do?

Is this anything to do with UUID's on the drives/partitions?

What parts do you have on the RAID drives?

How are the drives setup as RAID - as bare 
drives/partitions, or via LVG?



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