I've got a server running RHEL4, with a single (single-path) 195gig LUN attached. This weekend the storage team will be migrating the cisco switch for the SAN to new 9513 fibre channel switches. The concern is that the target id on the boxes may change when everything is brought back up.

Generally this isn't a huge deal. Requires a bit of work, but it can be worked around. The problem I have is that this particular server I administer was setup rather poorly. It's got 64gigs of physical storage. When that ran low, the 195gig LUN was made available, and it was added to the system volume group. So now I have SAN storage mixed in with the local storage. I believe (hope, pray, etc) that the SAN storage was only used to expand the /home lv. But is there anyway to determine this for certain? My concern is that if the LUN was used to expand anything else, the box may crater when we try to bring it back up and it doesn't see the same target id.

Some possibly helpful info:

bash-3.00# cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
Vendor: LSILOGIC Model: Logical Volume Rev: 3000
Type: Direct-Access ANSI SCSI revision: 02
Host: scsi2 Channel: 00 Id: 00 Lun: 00
Vendor: HITACHI Model: OPEN-V*4 Rev: 5008
Type: Direct-Access ANSI SCSI revision: 03
Host: scsi3 Channel: 00 Id: 00 Lun: 00
Vendor: AMI Model: Virtual CDROM Rev: 1.00
Type: CD-ROM ANSI SCSI revision: 02
Host: scsi4 Channel: 00 Id: 00 Lun: 00
Vendor: AMI Model: Virtual Floppy Rev: 1.00
Type: Direct-Access ANSI SCSI revision: 02


bash-3.00# vgdisplay -v
Finding all volume groups
Finding volume group "system"
--- Volume group ---
VG Name system
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 13
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 6
Open LV 5
Max PV 0
Cur PV 2
Act PV 2
VG Size 263.19 GB
PE Size 32.00 MB
Total PE 8422
Alloc PE / Size 5691 / 177.84 GB
Free PE / Size 2731 / 85.34 GB
VG UUID 1jbRtP-s9nD-QZkW-mcA3-kCSw-IwOT-2k4i0p

--- Logical volume ---
LV Name /dev/system/root
VG Name system
LV UUID euZ5Rv-GxYw-VBhu-sFRX-YenN-MK4f-eWLFJA
LV Write Access read/write
LV Status available
# open 1
LV Size 4.00 GB
Current LE 128
Segments 2
Allocation inherit
Read ahead sectors 0
Block device 253:0

--- Logical volume ---
LV Name /dev/system/home
VG Name system
LV UUID DzeEf4-jJi6-9TsI-dA1k-6Ahy-ehho-jEBEZG
LV Write Access read/write
LV Status available
# open 1
LV Size 152.34 GB
Current LE 4875
Segments 2
Allocation inherit
Read ahead sectors 0
Block device 253:1

--- Logical volume ---
LV Name /dev/system/tmp
VG Name system
LV UUID XiYeWr-XEI4-52rv-tYM4-NxkO-YZJh-MayX9d
LV Write Access read/write
LV Status available
# open 1
LV Size 512.00 MB
Current LE 16
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 253:2

--- Logical volume ---
LV Name /dev/system/usr
VG Name system
LV UUID QBq3cB-x8H7-dWr1-clBZ-2VsW-SqxT-1Q4359
LV Write Access read/write
LV Status available
# open 1
LV Size 16.00 GB
Current LE 512
Segments 2
Allocation inherit
Read ahead sectors 0
Block device 253:3

--- Logical volume ---
LV Name /dev/system/swap
VG Name system
LV UUID G7gHUk-PaJg-1PLC-W5k5-CtRh-zX7c-iL8mQK
LV Write Access read/write
LV Status available
# open 1
LV Size 4.00 GB
Current LE 128
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 253:4

--- Logical volume ---
LV Name /dev/system/opt
VG Name system
LV UUID t3zF9W-qno8-N1D9-H7tw-nrJ4-WheF-RRA1vM
LV Write Access read/write
LV Status available
# open 0
LV Size 1.00 GB
Current LE 32
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 253:5

--- Physical volumes ---
PV Name /dev/sda2
PV UUID J4apxp-VG4E-C3EJ-GDQb-dYuz-lpqo-thYR2D
PV Status allocatable
Total PE / Free PE 2172 / 1

PV Name /dev/sdb
PV UUID bvnwnC-LMff-r4hc-rjpR-KQ7f-6U3U-E85Axc
PV Status allocatable
Total PE / Free PE 6250 / 2730

bash-3.00# pvdisplay -v
Scanning for physical volume names
--- Physical volume ---
PV Name /dev/sda2
VG Name system
PV Size 67.88 GB / not usable 0
Allocatable yes
PE Size (KByte) 32768
Total PE 2172
Free PE 1
Allocated PE 2171
PV UUID J4apxp-VG4E-C3EJ-GDQb-dYuz-lpqo-thYR2D

--- Physical volume ---
PV Name /dev/sdb
VG Name system
PV Size 195.31 GB / not usable 0
Allocatable yes
PE Size (KByte) 32768
Total PE 6250
Free PE 2730
Allocated PE 3520
PV UUID bvnwnC-LMff-r4hc-rjpR-KQ7f-6U3U-E85Axc

------------------------------

If anyone has any advise for me I'd certainly appreciate it. I am making sure we get a full backup of this server before we do anything, but I am not sure how helpful that is going to be, to be honest.

~amy

and a follow-up question. Does the Segments number relate to the number of physical volumes? If so, I think I'm just going to lay down and cry.

Hi.

Ideally you could setup persistant bindings, but I dont know if this is possible in Redhat (I know this is not much help right).
I'm not sure how your LUNS are presented to the server either via WWPN or WWNN, but even if the device order changes I think LVM is smart enough to read the metedata and sort it out, (I'm guessing here from what I've seen). As well as a full backup you can dump the LVM information see : vgcfgbackup


Also have a look here, incase this happens : http://tldp.org/HOWTO/LVM-HOWTO/recovermetadata.html

Hope this helps sorry I dont have a real answer for you.

Thanks.. I'll look into that. We've scrapped the plans to move this one this weekend until we can sort this out. I am hopefully going to get my hands on a lab box today to re-create this then figure out how to un-do it.