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[dm-devel] Detecting Multiple Paths to LU



Hi Coates,

Thanks for the information.I am close to the solution now.

>>Once you assembled the multipath devices you can then run pvcreate
/dev/mapper/XXXXX  and create your volume groups.

But the only thing i am unable to understand is that how would I assemble
the multipath device?
who will do this for us LVM2 or Device mapper and how?
What are the steps I need to follow? What argument should I provide to
pvcreate as I had already filtered "sd" devices?
How would I create my assembled device "/dev/mapper/XXXXX"?
It would be very helpful if you could tell me what are the steps to create
assembled device "/dev/mapper/XXXXX". How this assembled device is mapped to
the underlying "sd" devices?


Regards
Shahid Shaikh.



-----Original Message-----
From: Guy Coates [mailto:gmpc sanger ac uk]
Sent: Wednesday, February 16, 2005 7:53 PM
To: shahid shaikh patni com; device-mapper development
Cc: Christophe Varoqui (E-mail); Sandhya Suman (E-mail)
Subject: Re: [dm-devel] Detecting Multiple Paths to LU



You need to set up lvm.conf to do the following. It probably is totally
correct, but it seems to work well enough.


# Make lvm look at the multipath device maps only, not the
# single devices

scan = [ "/dev/mapper" ]

# exclude the raw disks, just to be paranoid
filter = ["r|/dev/sd|"]

# make lvm use dm devices
types = [ "device-mapper", 16 ]


Once you assembled the multipath devices you can then run

pvcreate /dev/mapper/XXXXX

and create your volume groups.


I've created and then extended and LVM across two multipathed physical
volumes on my test system.



  --- Volume group ---
  VG Name               web409mysqltest
  System ID
  Format                lvm2
  Metadata Areas        2
  Metadata Sequence No  4
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                1
  Open LV               1
  Max PV                0
  Cur PV                2
  Act PV                2
  VG Size               199.99 GB
  PE Size               4.00 MB
  Total PE              51198
  Alloc PE / Size       51198 / 199.99 GB
  Free  PE / Size       0 / 0
  VG UUID               CzUDTb-KpRz-KNLS-U24P-5TmZ-4WLN-OSjGBB

  --- Logical volume ---
  LV Name                /dev/web409mysqltest/mysqltest1
  VG Name                web409mysqltest
  LV UUID                tT9PHO-1UVt-RsNN-6iFM-KgQx-Gl9r-adck9U
  LV Write Access        read/write
  LV Status              available
  # open                 2
  LV Size                199.99 GB
  Current LE             51198
  Segments               2
  Allocation             inherit
  Read ahead sectors     0
  Block device           254:16

  --- Physical volumes ---
  PV Name               /dev/mapper/3600508b40001417e0001c00001b60000
  PV UUID               3QvL3p-t45P-AY4x-nIHp-C44s-IM6O-2Ymuwy
  PV Status             allocatable
  Total PE / Free PE    25599 / 0

  PV Name               /dev/mapper/3600508b40001417e0001c00001c90000
  PV UUID               QGEVaA-W3sJ-DkLB-Ble1-13sU-bL6u-3tNy78
  PV Status             allocatable
  Total PE / Free PE    25599 / 0



/sbin/dmsetup  status  /dev/mapper/3600508b40001417e0001c00001c90000
0 209715200 multipath 1 0 0 2 2 E 0 2 0 65:240 A 0 8:176 A 0 E 0 2 0 8:16 A
0 65:80 A 0

 /sbin/dmsetup  status /dev/mapper/3600508b40001417e0001c00001b60000
0 209715200 multipath 1 0 0 2 2 E 0 2 0 65:224 A 0 8:160 A 0 E 0 2 0 8:0 A 0
65:64 A 0



lvm version report

lvm version
  LVM version:     2.00.24 (2004-09-16)
  Library version: 1.00.19-ioctl (2004-07-03)
  Driver version:  4.3.0


Guy


--
Dr. Guy Coates,  Informatics System Group
The Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1SA, UK
Tel: +44 (0)1223 834244 ex 7199



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