Hi Hertha, How to find out minor device of a major device (for entry in rawdevices file)

[sunhux G]

Hi Hertha/anyone else,


Thanks, there's actually four paths
(as 2 SAN switches x 2 fibre cables = 4 possible paths).


Just four more questions :

a) does it serve any purpose to enter the minor devices (in my
    case there's 4 of them) into rawdevices file?  (Say, will this
    tell Linux that in the event one path is down, it will take the
    next available logical/minor device    or    will it help spread
    the traffic load between the paths?)

b) I can use fdisk /dev/mpath/mpathx, select "p" (partition) to
    find out the disk capacity of each of the logical mpathx
    device.  However, "df -k /dev/mpath/mpathx"  will not show
    the true capacity.  If I have more than 10 of those logical
    devices, this is going to be tedious.  Is there a faster/shorter
    way to find out the capacities?

c) if one of the four paths is broken for some reason, I suppose
    that's when "multipath -ll" will show one path less.  How
    can I find out which path needs replacement/fixing when
    this happens?

d) Last question is probably a SAN (Netapp) question :
    how can I find out from Linux end, which physical disk in
    the SAN is faulty

"multipath -ll"  output follows for one of the logical device :

mpath0 (360a9800056724439633449336c786d69)
[size=5 GB][features="1 queue_if_no_path"][hwhandler="0"]
\_ round-robin 0 [prio=8][enabled]
 \_ 8:0:2:4 sdr 65:16  [active][ready]
 \_ 8:0:3:4 sdx 65:112 [active][ready]
\_ round-robin 0 [prio=2][enabled]
 \_ 8:0:0:4 sdf 8:80   [active][ready]
 \_ 8:0:1:4 sdl 8:176  [active][ready]


Thanks a lot
U

On 5/20/08, Herta Van den Eynde <herta.vandeneynde at gmail.com> wrote:
>
> 2008/5/20 sunhux G <sunhux at gmail.com>:
> > Hi Hertha,
> >
> >
> > Thanks.
> > Noticed that in the rawdevices file, there's column for minor device
> > file name.
> >
> > I heard for each of the /dev/mpath/mpathx, there's actually
> > two corresponding
> > minor devices (/dev/sd...).
> >
> > Yes, 2 /dev/sdx  devices are the actual physical path to the SAN while
> > /dev/mpath/mpathx is the logical path with redundancy (ie if one physical
> > path is down, it will use the other path).
> >
> > How do I find out the physical paths for a logical path?
> >
> >
> > Tks
> > U
>
> Depending on how the SAN is configured you may even have more that 2
> physical paths to a logical device.
> You should be able to see the mapping using the command 'multipath -ll'.
>
> Kind regards,
>
> Herta
>
> --
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