LVM and hardware device re-ordering?
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
Quoted 8 lines · Don Buchholz
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,
Signature · 11 lines
AJ Lewis Voice: 612-638-0500 Red Hat Inc. E-Mail: [email protected] 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---------------------------------------- Computers make very fast, very accurate mistakes. -----End Obligatory Humorous Quote------------------------------------------
Thanks, AJ.
May I propose this question for inclusion in the LVM HOWTO FAQ chapter?
- Don
Quoted 35 lines · AJ Lewis
Quoted 10 lines · Don Buchholz
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,
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Quoted 1 line · Don Buchholz
May I propose this question for inclusion in the LVM HOWTO FAQ chapter?
Yep - I was planning on doing that. :)
Regards,
Signature · 11 lines
AJ Lewis Voice: 612-638-0500 Red Hat Inc. E-Mail: [email protected] 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------------------------------------------