[linux-lvm] LVM and hardware device re-ordering?

[linux-lvm] LVM and hardware device re-ordering?

[Don Buchholz]

I'm looking at implementing my first LVM system.  It looks
pretty straight-forward.  (Very similar to the LVM stuff I
saw in AIX v3.x and Veritas management Sun used to manage
SPARCStorage Arrays.)

The one nagging question in my mind is:

  How resilient is LVM to a sudden renumbering of
  physical hard disks?

Assume no disks have actually failed, just that a new disk
gets added and suddenly all the LVM drives get notched up
a drive letter. 

For example,

 Before  After  SCSI ID*    description
 ------  -----  --------   --------------------------------
   sda    sda    0,0,0,0    operating system disk (HW RAID)
    --    sdb    0,0,1,0    new added disk (e.g. a CD drive)

   sdb    sdc    1,0,0,0    LVM PV#1
   sdc    sdd    1,0,0,1    LVM PV#2
   sdd    sde    1,0,0,2    LVM PV#3
 ----------------------------------------------------------
  * The four numbers are:  (1) controller, (2) controller
   channel, (3) SCSI target, (4) SCSI LUN.

Can I just assume LVM will do the right thing, and my VG
created from the three physical volumes will be OK?

Thanks,
- Don Buchholz

Re: [linux-lvm] LVM and hardware device re-ordering?

[AJ Lewis]

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On Fri, Apr 30, 2004 at 08:55:32AM -0700, Don Buchholz wrote:
> The one nagging question in my mind is:
> 
>  How resilient is LVM to a sudden renumbering of
>  physical hard disks?
> 
> Assume no disks have actually failed, just that a new disk
> gets added and suddenly all the LVM drives get notched up
> a drive letter. 

It's fine.  Each disk (PV) is labeled with a UUID, which uniquely identifies
it to the system.  'vgscan' identifies this after a new disk is added that
changes your drive numbering.  Most distros run vgscan in the lvm startup
scripts to cope with this on reboot after a hardware addition.  If you're
doing a hot-add, you'll have to run this by hand I think.  OTOH, if your vg
is activated and being used, the renumbering should not affect it at all.
It's only the activation that needs the identifier, and the worst case
scenario is that the activation will fail without a vgscan with a complaint
about a missing PV.

Regards,
-- 
AJ Lewis                                   Voice:  612-638-0500
Red Hat Inc.                               E-Mail: alewis@redhat.com
720 Washington Ave. SE, Suite 200
Minneapolis, MN 55414

Current GPG fingerprint = FE77 4B43 6A9B F982 A731  02FA 2BF5 7574 294A AA5A
Grab the key at: http://people.redhat.com/alewis/gpg.html or one of the
many keyservers out there...
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Re: [linux-lvm] LVM and hardware device re-ordering?

[Don Buchholz]

Thanks, AJ.

May I propose this question for inclusion in the LVM HOWTO FAQ chapter?

- Don

AJ Lewis wrote:

>On Fri, Apr 30, 2004 at 08:55:32AM -0700, Don Buchholz wrote:
>  
>
>>The one nagging question in my mind is:
>>
>> How resilient is LVM to a sudden renumbering of
>> physical hard disks?
>>
>>Assume no disks have actually failed, just that a new disk
>>gets added and suddenly all the LVM drives get notched up
>>a drive letter. 
>>    
>>
>
>It's fine.  Each disk (PV) is labeled with a UUID, which uniquely identifies
>it to the system.  'vgscan' identifies this after a new disk is added that
>changes your drive numbering.  Most distros run vgscan in the lvm startup
>scripts to cope with this on reboot after a hardware addition.  If you're
>doing a hot-add, you'll have to run this by hand I think.  OTOH, if your vg
>is activated and being used, the renumbering should not affect it at all.
>It's only the activation that needs the identifier, and the worst case
>scenario is that the activation will fail without a vgscan with a complaint
>about a missing PV.
>
>Regards,
>  
>
>------------------------------------------------------------------------
>
>_______________________________________________
>linux-lvm mailing list
>linux-lvm@redhat.com
>https://www.redhat.com/mailman/listinfo/linux-lvm
>read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>

Re: [linux-lvm] LVM and hardware device re-ordering?

[AJ Lewis]

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On Fri, Apr 30, 2004 at 10:43:42AM -0700, Don Buchholz wrote:
> May I propose this question for inclusion in the LVM HOWTO FAQ chapter?

Yep - I was planning on doing that.  :)

Regards, 
-- 
AJ Lewis                                   Voice:  612-638-0500
Red Hat Inc.                               E-Mail: alewis@redhat.com
720 Washington Ave. SE, Suite 200
Minneapolis, MN 55414

Current GPG fingerprint = FE77 4B43 6A9B F982 A731  02FA 2BF5 7574 294A AA5A
Grab the key at: http://people.redhat.com/alewis/gpg.html or one of the
many keyservers out there...
-----Begin Obligatory Humorous Quote----------------------------------------
Mountain Dew... because breakfast is the most important meal of the day.
-----End Obligatory Humorous Quote------------------------------------------

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