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



Yes, the dm names are the aliases I set-up in the multipathd.conf and
should not change.
I listed these below in my initial email.  In this example the alias is
called: dm-5_0111

# multipath -ll
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]

Corresponding entry in multipathd.conf:
multipath  {
                wwid    360060480000290300618533030313131
                alias   dm-5_0111
                }

S.


brem belguebli wrote:
> What you have to be aware of is that /dev/dm names are volatile and
> can change across reboots as are /dev/sd names, never use them
> directly.
>
> If you are using device-mapper-multipath (not emcpowerpath) there is a
> "user_friendly_names" boolean setting in /etc/multipath.conf that
> would give you names such as /dev/mpath/mpath0 is set to yes.
>
> If set to no, it would give you names such as /dev/mpath/UUID.
>
> Both namings are persistent (stable across reboots) as multipath will
> base its binding on the disk UUID.
>
> see man multipath.conf to have full options listing.
>
> It allows you also to give custom names to devices by using the alias
> setting in multipath.conf.
>
> The filter you applied (your previous email) just prevents "r/..." LVM
> to check and so activate the device names that you rejected.
>
> Hope this'll help
>
> 2009/12/30 Simon Loewenthal/NL/Tele2 <simon loewenthal klunky co uk>:
>   
>> 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 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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>>>>
>>>>
>>>>         
>>> _______________________________________________
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>>>
>>>       
>> _______________________________________________
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>>
>>     
>
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