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Re: [linux-lvm] LVM preference for multipath verses disk/by-id/scsi



I don't think this original Email made it through to the list, but I
think I have found an solution:

In lvm.conf there is this line,
filter = [ "r|/dev/.*/by-path/.*|", "r|/dev/.*/by-id/.*|", "a/.*/" ]

If I remove the portion "r|/dev/.*/by-id/.*|", so it is rewritten as,
filter = [ "r|/dev/.*/by-path/.*|", "a/.*/" ]
...then it ought to ignore the device,
/dev/disk/by-id/scsi-360060480000290300618533030313133

Is this correct?

S.

-- 
Simon Loewenthal/Tele2


Simon Loewenthal/NL/Tele2 wrote:
> Dear all,
>
>     I have a volume group that is currently using discs directly
> presented from EMC e.g
> /dev/disk/by-id/scsi-360060480000290300618533030313042 .
>
> An lvdisplay -v shows these PVs:
> # vgdisplay -v vg_mds
>     Using volume group(s) on command line
>     Finding volume group "vg_mds"
>   --- Volume group ---
>   VG Name               vg_mds
>   System ID            
>   Format                lvm2
>   Metadata Areas        12
>   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                12
>   Act PV                12
>   VG Size               202.12 GB
>   PE Size               32.00 MB
>   Total PE              6468
>   Alloc PE / Size       6468 / 202.12 GB
>   Free  PE / Size       0 / 0  
>   VG UUID               Wnk1a8-xdVf-RorP-ZxPE-Z3D9-5fp1-2o4hHs
>   
>   --- Logical volume ---
>   LV Name                /dev/vg_mds/lvol_mds
>   VG Name                vg_mds
>   LV UUID                TErCZW-senu-YR3k-I25n-Tqk9-BK2k-3mQY3S
>   LV Write Access        read/write
>   LV Status              available
>   # open                 1
>   LV Size                202.12 GB
>   Current LE             6468
>   Segments               12
>   Allocation             inherit
>   Read ahead sectors     0
>   Block device           253:7
>   
>   --- Physical volumes ---
>   PV Name              
> /dev/disk/by-id/scsi-360060480000290300618533030313133    
>   PV UUID               255V1X-uMZp-Lod1-3jsa-cCGd-JaNZ-v0dEXn
>   PV Status             allocatable
>   Total PE / Free PE    539 / 0
>   
>   PV Name              
> /dev/disk/by-id/scsi-360060480000290300618533030313131    
>   PV UUID               RU5WZK-G3hY-lXCD-F6Kj-PcJA-DcbE-iV17P7
>   PV Status             allocatable
>   Total PE / Free PE    539 / 0
>   
>   PV Name              
> /dev/disk/by-id/scsi-360060480000290300618533030313046    
>   PV UUID               c3DVym-lzdw-MgS6-acQI-BcUD-UOGq-iG6hSe
>   PV Status             allocatable
>   Total PE / Free PE    539 / 0
>   
>   PV Name              
> /dev/disk/by-id/scsi-360060480000290300618533030313044    
>   PV UUID               d7VD54-KmXZ-t8eX-dvph-9lSp-ym03-Lc62sI
>   PV Status             allocatable
>   Total PE / Free PE    539 / 0
>   
>   PV Name              
> /dev/disk/by-id/scsi-360060480000290300618533030313042    
>   PV UUID               n32oAY-soe3-odYI-SAFQ-yM7v-FRaw-e9hS63
>   PV Status             allocatable
>   Total PE / Free PE    539 / 0
>   
>   PV Name              
> /dev/disk/by-id/scsi-360060480000290300618533030313039    
>   PV UUID               hT2hZ7-XAZr-ZUte-rzLV-kwFX-Jtih-K3OgZe
>   PV Status             allocatable
>   Total PE / Free PE    539 / 0
>   
>   PV Name              
> /dev/disk/by-id/scsi-360060480000290300618533030313037    
>   PV UUID               ut4fEx-R0c2-lA4y-qS3F-SYfp-Chuz-2SrvTo
>   PV Status             allocatable
>   Total PE / Free PE    539 / 0
>   
>   PV Name              
> /dev/disk/by-id/scsi-360060480000290300618533030313035    
>   PV UUID               BMJ8LA-b0L7-aAoK-4WqG-MLdU-s8Y8-xGib2s
>   PV Status             allocatable
>   Total PE / Free PE    539 / 0
>   
>   PV Name              
> /dev/disk/by-id/scsi-360060480000290300618533030313033    
>   PV UUID               uSasZ1-96rT-ngGN-Wfcr-fBNg-ceM0-GaccVU
>   PV Status             allocatable
>   Total PE / Free PE    539 / 0
>   
>   PV Name              
> /dev/disk/by-id/scsi-360060480000290300618533030313031    
>   PV UUID               R15yAf-t1YO-Z0Dx-4n2G-oTyD-Secp-2igMJc
>   PV Status             allocatable
>   Total PE / Free PE    539 / 0
>   
>   PV Name              
> /dev/disk/by-id/scsi-360060480000290300618533030304646    
>   PV UUID               nrhhx1-7AxM-VmVv-sRY5-TLR7-UAEE-wBUIMB
>   PV Status             allocatable
>   Total PE / Free PE    539 / 0
>   
>   PV Name              
> /dev/disk/by-id/scsi-360060480000290300618533030304644    
>   PV UUID               ctz8rd-ew58-0pU8-FssR-x9pR-KSA9-mI4flw
>   PV Status             allocatable
>   Total PE / Free PE    539 / 0
>
>
> I want to export this volume group and inport it again using
> multipathing.  I have configured the multipathing thus,
>  # multipath -ll
> dm-6_010F (360060480000290300618533030313046) dm-6 EMC,SYMMETRIX
> [size=17G][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:31 sdx        65:112 [active][ready]
>  \_ 1:0:0:31 sdk        8:160  [active][ready]
> dm-17_0012 (360060480000290300618533030303132) dm-17 EMC,SYMMETRIX
> [size=4.7M][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:0  sdn        8:208  [active][ready]
>  \_ 1:0:0:0  sda        8:0    [active][ready]
> dm-13_0103 (360060480000290300618533030313033) dm-13 EMC,SYMMETRIX
> [size=17G][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:25 sdr        65:16  [active][ready]
>  \_ 1:0:0:25 sde        8:64   [active][ready]
> dm-10_0109 (360060480000290300618533030313039) dm-10 EMC,SYMMETRIX
> [size=17G][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:28 sdu        65:64  [active][ready]
>  \_ 1:0:0:28 sdh        8:112  [active][ready]
> dm-14_0101 (360060480000290300618533030313031) dm-14 EMC,SYMMETRIX
> [size=17G][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:24 sdq        65:0   [active][ready]
>  \_ 1:0:0:24 sdd        8:48   [active][ready]
> dm-8_010D (360060480000290300618533030313044) dm-8 EMC,SYMMETRIX
> [size=17G][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:30 sdw        65:96  [active][ready]
>  \_ 1:0:0:30 sdj        8:144  [active][ready]
> dm-15_00FF (360060480000290300618533030304646) dm-15 EMC,SYMMETRIX
> [size=17G][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:23 sdp        8:240  [active][ready]
>  \_ 1:0:0:23 sdc        8:32   [active][ready]
> dm-11_0107 (360060480000290300618533030313037) dm-11 EMC,SYMMETRIX
> [size=17G][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:27 sdt        65:48  [active][ready]
>  \_ 1:0:0:27 sdg        8:96   [active][ready]
> dm-4_0113 (360060480000290300618533030313133) dm-4 EMC,SYMMETRIX
> [size=17G][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:33 sdz        65:144 [active][ready]
>  \_ 1:0:0:33 sdm        8:192  [active][ready]
> dm-9_010B (360060480000290300618533030313042) dm-9 EMC,SYMMETRIX
> [size=17G][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:29 sdv        65:80  [active][ready]
>  \_ 1:0:0:29 sdi        8:128  [active][ready]
> dm-16_00FD (360060480000290300618533030304644) dm-16 EMC,SYMMETRIX
> [size=17G][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:22 sdo        8:224  [active][ready]
>  \_ 1:0:0:22 sdb        8:16   [active][ready]
> dm-12_0105 (360060480000290300618533030313035) dm-12 EMC,SYMMETRIX
> [size=17G][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:26 sds        65:32  [active][ready]
>  \_ 1:0:0:26 sdf        8:80   [active][ready]
> dm-5_0111 (360060480000290300618533030313131) dm-5 EMC,SYMMETRIX
> [size=17G][features=0][hwhandler=0]
> \_ round-robin 0 [prio=2][active]
>  \_ 0:0:0:32 sdy        65:128 [active][ready]
>  \_ 1:0:0:32 sdl        8:176  [active][ready]
>
> Device mapper reports this:
> # dmsetup ls
> dm-6_010F    (253, 6)
> dm-17_0012    (253, 17)
> dm-13_0103    (253, 13)
> dm-10_0109    (253, 10)
> vg00-app052    (253, 3)
> vg00-xen    (253, 2)
> vg00-usr    (253, 0)
> vg00-var    (253, 1)
> dm-14_0101    (253, 14)
> dm-8_010D    (253, 8)
> dm-15_00FF    (253, 15)
> dm-11_0107    (253, 11)
> dm-4_0113    (253, 4)
> vg_mds-lvol_mds    (253, 7)
> dm-9_010B    (253, 9)
> dm-16_00FD    (253, 16)
> dm-12_0105    (253, 12)
> dm-5_0111    (253, 5)
>
>
> What I do not understand is that surly when I perform a vgscan how will
> it decide to query only the devices presented from the multipathd, and
> ignore those presented via the dev/disk/by-id/scsi-nnnnnnnnnn?  Won't it
> see two vg_mds volumes instead of only those volumes that lie on the
> multipathed discs, which are the same pshycial discs as the disk/by-id?
>
> My plan of action is currently:
>     vgchange -a n vg_mds
>     vgexport -m /tmp/vg_mds.map mds
>     vgexport -f /tmp/vg_mds.pv mds
>     vgscan
>     vgchange -y a vg_mds
>     vgimport vg_mds /*OR instead do it the long way on the next line*  /
>         vgscan
>         mkdir /dev/vg_mds
>         mknod /dev/vg_mds/group c 64 0xNN0000
>         vgimport -v -s -m /tmp/vg_mds.map /dev/vg_mds
>
> I do not see how to tell it to ignore the non-multipathed disc, or has
> multipathd or LVM have some preference for mutlipath discs over
> non-multipathed discs, and if so then what is the logic behind the decision?
>
> Any help to further my understanding would be gratefully appreciated.
>
> Best wishes, S.
>
> PS. I am using SLES, but this was the only mailinglist I found for LVM
> so I subscribed to it.  I think that LVM and multipathd implementations
> are reasonably similar across Linux distos. Ergo concepts here are
> applicable to Suse.  The kernel I am using is a xen enabled host (not a
> guest): 2.6.16.60-0.27-xen #1 SMP.
>
>   

-- 
Simon Loewenthal/Tele2

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