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

Simon Loewenthal/NL/Tele2 simon.loewenthal at klunky.co.uk
Wed Dec 30 12:37:25 UTC 2009


Thank-you Bren for the info., I am unsure how to specify the
preferred_devices using the muttipath:
 Should it be:

preferred_names = [ "^/dev/dm-*/" , "^/dev/cciss/" ]


so that it uses these discs :
/dev/cciss/c0d0p4  (internal disc)
dm-6_010F	(multipathd alias for EMC disc)
dm-17_0012	(multipathd alias for EMC disc)
dm-13_0103	(multipathd alias for EMC disc)
dm-10_0109	(multipathd alias for EMC disc)

The EMC discs are listed under /dev as :
 # ls -l /dev/dm-?
brw-r----- 1 root disk 253, 0 Oct 26 14:44 /dev/dm-0
brw-r----- 1 root disk 253, 1 Oct 26 14:44 /dev/dm-1
brw-r----- 1 root disk 253, 2 Oct 26 14:44 /dev/dm-2
brw-r----- 1 root disk 253, 3 Oct 30 10:16 /dev/dm-3
brw-r----- 1 root disk 253, 4 Dec  4 11:47 /dev/dm-4
brw-r----- 1 root disk 253, 5 Dec  4 11:47 /dev/dm-5
brw-r----- 1 root disk 253, 6 Dec  4 11:47 /dev/dm-6
brw-r----- 1 root disk 253, 7 Oct 26 14:44 /dev/dm-7
brw-r----- 1 root disk 253, 8 Dec  4 11:47 /dev/dm-8
brw-r----- 1 root disk 253, 9 Dec  4 11:47 /dev/dm-9

...but I do not see /dev/dm-6_010F. 


S.



brem belguebli wrote:
> Hi,
>
> see man 5 lvm.conf there is an option called preferred_names which is
> well explained
>
> It'll instruct lvm to use the preferred_names you configured in the
> lvm.conf file if they exist
>
> ie : preferred_names = "/dev/mpath/" will use /dev/mpath/XXX instead
> of /dev/mapper/XXX
>
>
> 2009/12/30 Simon Loewenthal/NL/Tele2 <simon.loewenthal at tele2.com>:
>   
>> 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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