topic Re: powerpath linux alternate path in Operating System - Linux

powerpath linux alternate path

Gerrit_1 — Mon, 04 Jul 2005 06:07:55 GMT

Hi,
I've installed powerpath 4.3.1 on a linux RH3.0
update 5.

I've added one lun (from a cx600), this gives me :

root/svlirc13# powermt display dev=all
Pseudo name=emcpowera
CLARiiON ID=CK200033400080 [Linux_svlirc13]
Logical device ID=60060160A3F30D007AFB85F315AED811 [LUN 138]
state=alive; policy=BasicFailover; priority=0; queued-IOs=0
Owner: default=SP A, current=SP A
==============================================================================
---------------- Host --------------- - Stor - -- I/O Path - -- Stats ---
### HW Path I/O Paths Interf. Mode State Q-IOs Errors
==============================================================================
1 lpfc sdc SP B0 active alive 0 0
1 lpfc sdd SP A0 active alive 0 0

I think this is ok.

But when I create a volumegroup I can't vgextend with the alternate path.

root/svlirc13# vgdisplay -v vg_test
--- Volume group ---
VG Name vg_test
VG Access read/write
VG Status available/resizable
VG # 1
MAX LV 256
Cur LV 0
Open LV 0
MAX LV Size 2 TB
Max PV 256
Cur PV 1
Act PV 1
VG Size 65.94 GB
PE Size 32 MB
Total PE 2110
Alloc PE / Size 0 / 0
Free PE / Size 2110 / 65.94 GB
VG UUID xlMTyK-Kdvw-wpw4-GHXN-BvyP-7ubS-Z0urG0

--- No logical volumes defined in "vg_test" ---

--- Physical volumes ---
PV Name (#) /dev/sdc1 (1)
PV Status available / allocatable
Total PE / Free PE 2110 / 2110

root/svlirc13# vgextend vg_test /dev/sdd1
vgextend -- INFO: maximum logical volume size is 2 Terabyte
vgextend -- ERROR: "/dev/sdd1" is not a new physical volume

What I'm doing wrong?

Tx.

Re: powerpath linux alternate path

Donald Kok — Mon, 04 Jul 2005 06:18:40 GMT

Hi Gerrit,
You should do a pvcreate first before you do a vgextend.
Groeten
Donald

Re: powerpath linux alternate path

Gerrit_1 — Mon, 04 Jul 2005 06:30:37 GMT

Also on the alternate path?
This is what I've done.

root/svlirc13# fdisk /dev/sdc
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel. Changes will remain in memory only,
until you decide to write them. After that, of course, the previous
content won't be recoverable.

The number of cylinders for this disk is set to 8615.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-8615, default 1):
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-8615, default 8615):
Using default value 8615

Command (m for help): t
Selected partition 1
Hex code (type L to list codes): 8e
Changed system type of partition 1 to 8e (Linux LVM)

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

root/svlirc13# pvcreate /dev/sdc1
pvcreate -- physical volume "/dev/sdc1" successfully created

root/svlirc13# vgcreate vg_test /dev/sdc1
vgcreate -- INFO: using default physical extent size 32 MB
vgcreate -- INFO: maximum logical volume size is 2 Terabyte
vgcreate -- doing automatic backup of volume group "vg_test"
vgcreate -- volume group "vg_test" successfully created and activated

root/svlirc13# vgextend vg_test /dev/sdd1
vgextend -- INFO: maximum logical volume size is 2 Terabyte
vgextend -- ERROR: "/dev/sdd1" is not a new physical volume

Re: powerpath linux alternate path

Matti_Kurkela — Mon, 04 Jul 2005 08:39:10 GMT

You're probably thinking with a mental model of HP-UX LVM. Linux is a bit different: on Linux, LVM does not handle multiple paths.

The vgextend command is giving you an error message because it notices you're trying to add the same PV to the VG twice.

Disclaimer: I've never used PowerPath on HP-UX, but I've successfully implemented a FibreChannel failover using native Linux multipath support (still somewhat experimental, I think). I have PowerPath on HP-UX but the manuals are not quite handy and the PowerPath manpages are rather terse.

The devices /dev/sdc and /dev/sdd refer to one path each. The kernel does not know that both these paths lead to the same piece of storage. You need something that means "either /dev/sdc or /dev/sdd or both, whatever works best". PowerPath is supposed to give you that, because it understands multiple paths and can do load balancing between them.

If I understood correctly how PowerPath is supposed to work on Linux, the line "Pseudo name=emcpowera" is a vital clue. The "powermt" command seems to be telling you that "emcpowera" is a wrapper that contains /dev/sdc and /dev/sdd.

If the device "/dev/emcpowera" exists, leave
/dev/sdc and /dev/sdd alone, and create your VG on /dev/emcpowera instead.

If it does not exist, my educated guess is probably wrong...

Re: powerpath linux alternate path

Gerrit_1 — Mon, 04 Jul 2005 09:05:57 GMT

Tx,

root/svlirc13# fdisk -l /dev/emcpowera

Disk /dev/emcpowera: 70.8 GB, 70866960384 bytes
255 heads, 63 sectors/track, 8615 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/emcpowera1 1 8615 69199956 8e Linux LVM

But when I try to :

root/svlirc13# pvcreate /dev/emcpowera1
pvcreate -- invalid physical volume "/dev/emcpowera1"