[linux-lvm] Mirror between different SAN fabrics

[Christian.Rohrmeier at SCHERING.DE]

Hi,

Here is a nice example from one of my RHEL 4 Oracle servers:

We have three layers:

first the LUNs from the SAN are multipathed to device aliases:

[root@ ~]# multipath -ll
sanb (XXXX60e8003f653000000XXXX000001c7)
[size=101 GB][features="1 queue_if_no_path"][hwhandler="0"]
\_ round-robin 0 [active]
 \_ 0:0:1:1 sdb 8:16 [active][ready]
 \_ 1:0:1:1 sdd 8:48 [active][ready]

sana (XXXX60e80039cbe000000XXXX000006ad)
[size=101 GB][features="1 queue_if_no_path"][hwhandler="0"]
\_ round-robin 0 [active]
 \_ 0:0:0:1 sda 8:0  [active][ready]
 \_ 1:0:0:1 sdc 8:32 [active][ready]

Next these multipath aliases are RAIDed:

[root@ ~]# mdadm --detail /dev/md0
/dev/md0:
        Version : 00.90.01
  Creation Time : Thu Nov  2 13:07:01 2006
     Raid Level : raid1
     Array Size : 106788160 (101.84 GiB 109.35 GB)
    Device Size : 106788160 (101.84 GiB 109.35 GB)
   Raid Devices : 2
  Total Devices : 2
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Thu Dec 28 09:36:19 2006
          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0


    Number   Major   Minor   RaidDevice State
       0     253        2        0      active sync   /dev/mapper/sana
       1     253        3        1      active sync   /dev/mapper/sanb
           UUID : b5ac4ae9:99da8114:744a7ebb:aba6f687
         Events : 0.4254576

And finally, the RAID device is used with LVM:

[root@ ~]# vgs -o +devices
  VG   #PV #LV #SN Attr   VSize   VFree Devices
  vg00   2   2   0 wz--n-  31.78G    0  /dev/cciss/c0d0p2(0)
  vg00   2   2   0 wz--n-  31.78G    0  /dev/cciss/c0d0p4(0)
  vg00   2   2   0 wz--n-  31.78G    0  /dev/cciss/c0d0p2(250)
  vg01   1   5   0 wz--n- 101.84G    0  /dev/md0(0)
  vg01   1   5   0 wz--n- 101.84G    0  /dev/md0(5120)
  vg01   1   5   0 wz--n- 101.84G    0  /dev/md0(5376)
  vg01   1   5   0 wz--n- 101.84G    0  /dev/md0(5632)
  vg01   1   5   0 wz--n- 101.84G    0  /dev/md0(8192)

This works very well, as both paths and mirrors are able to break away
without any disruption in disk access.

Cheers,

Christian


                                                                           
             <mathias.herzog at p                                             
             ostfinance.ch>                                                
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                                                                   Subject 
             28.12.2006 09:12          RE: [linux-lvm] Mirror between      
                                       different SAN fabrics               
                                                                           
             Please respond to                                             
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             <linux-lvm at redhat                                             
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> -----Original Message-----
> From: linux-lvm-bounces at redhat.com
> [mailto:linux-lvm-bounces at redhat.com] On Behalf Of Matt P
[...]
> I think the proper way would be to use mdadm. Setup software
> RAID1 prior to getting LVM involved...
That sounds like a good solution. So far I don't know mdadm but I'm
already getting into it

Thanks, Mathias

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