persistent device names on rhel4

persistent device names on rhel4

[lnx dm]

I am using multipathing on rhel4 u3 x86_64 with
EVA4000 and HSV200 controller.

I had a few questions:

1. lsmod shows the below modules 

dm_mirror              29017  0
dm_round_robin          4929  1
dm_multipath           21841  2 dm_round_robin
dm_mod                 67457  9 dm_mirror,dm_multipath

Do need to insert "multipath" module also ?
If yes then what it is for ?

without using multipath module I can see multiple
paths in multipath -v2 -l output

2. How do I ensure that the same device gets mounted
across reboots ?
I verified that across the reboots mpath6 refers to
the same device, wwid is same for mpath6 across
reboots

# multipath -v2 -l
mpath6 (3600805f300176640a435a927359c0003)
[size=440 GB][features="0"][hwhandler="0"]
\_ round-robin 0 [active]
 \_ 2:0:0:1     sdag 66:0   [active][ready]
 \_ 0:0:0:1     sda  8:0    [active][ready]

I have /dev/mapper/mpath6 in /etc/fstab and it works
correctly.

# ls -l /dev/mpath/mpath6
lrwxrwxrwx  1 root root 7 Jul 18 06:13
/dev/mpath/mpath6 -> ../dm-6

What is the difference if I use /dev/dm-6 ?

which will be better ?

Thanks.

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Re: persistent device names on rhel4

[Benjamin Marzinski]

On Tue, Jul 18, 2006 at 06:32:42AM -0700, lnx dm wrote:
> I am using multipathing on rhel4 u3 x86_64 with
> EVA4000 and HSV200 controller.
> 
> I had a few questions:
> 
> 1. lsmod shows the below modules 
> 
> dm_mirror              29017  0
> dm_round_robin          4929  1
> dm_multipath           21841  2 dm_round_robin
> dm_mod                 67457  9 dm_mirror,dm_multipath
> 
> Do need to insert "multipath" module also ?
> If yes then what it is for ?

The modules that you see in the lsmod should be all you need.
 
> without using multipath module I can see multiple
> paths in multipath -v2 -l output
> 
> 2. How do I ensure that the same device gets mounted
> across reboots ?
> I verified that across the reboots mpath6 refers to
> the same device, wwid is same for mpath6 across
> reboots

mpath6 will always point to the same device on that node.  If you have multiple
nodes using the same devices, and you want to make sure that they all use the
same multipath names, you can just copy the /var/lib/multipath/bindings file
from a node where the names are set up the way you want to the other nodes.
This file holds the WWID -> user_friendly_name bindings.

> # multipath -v2 -l
> mpath6 (3600805f300176640a435a927359c0003)
> [size=440 GB][features="0"][hwhandler="0"]
> \_ round-robin 0 [active]
>  \_ 2:0:0:1     sdag 66:0   [active][ready]
>  \_ 0:0:0:1     sda  8:0    [active][ready]
> 
> I have /dev/mapper/mpath6 in /etc/fstab and it works
> correctly.
> 
> # ls -l /dev/mpath/mpath6
> lrwxrwxrwx  1 root root 7 Jul 18 06:13
> /dev/mpath/mpath6 -> ../dm-6
> 
> What is the difference if I use /dev/dm-6 ?

There is now way to guarantee the /dev/dm-6 will always refer to the correct
device.

> which will be better ?

mpath6

> Thanks.
> 
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