My Lazy Admin: Multipath

Basics

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- configuration is stored in /etc/multipath.conf

Things to note in modifying multipath.conf

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1. Make sure letters in WWIDs are in lower case. If not, multipath will blacklist them.

2. Make sure WWIDs don't have more than 1 size. If there is, delete the other device.

It will reject the the WWID if it sees conflict like this:

reject: ibmdata1 (3600507680c810200e000000000000027) undef IBM,2145

Parts of the "multipath -ll" output

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data3 (360000970000198701142533030413536) dm-4 EMC,SYMMETRIX --> data3 is the multipath device

size=512G features='1 queue_if_no_path' hwhandler='0' wp=rw

`-+- policy='round-robin 0' prio=1 status=active

|- 2:0:1:4 sdj 8:144 active ready running --> path #1

|- 2:0:0:4 sde 8:64 active ready running --> path #2

|- 1:0:0:4 sdo 8:224 active ready running --> path #3

`- 1:0:1:4 sdt 65:48 active ready running --> path #4

Multipath in Virtual Machines

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In virtual machines, even if direct disk addressing (in VmWare terms raw device

mapping) is used, the underling virtualisation hypervisor handles multipathing

and masks it from the client virtual machine. Thus virtual machine itself

doesn't need to do anything about it.

Tutorials

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Determining LUN ID

Inspect "multipath -ll" output. Last number (in X:X:X:X) is the LUN ID.

That LUN ID is the one you will see on the storage array.

U01 (3624a9370b15fcb83b6a947a00001d5e7) dm-2 PURE ,FlashArray

size=150G features='0' hwhandler='0' wp=rw

`-+- policy='queue-length 0' prio=1 status=active

|- 2:0:0:2 sdk 8:160 active ready running

|- 2:0:1:2 sdo 8:224 active ready running

|- 1:0:0:2 sdc 8:32 active ready running

My Lazy Admin