[Linux-cluster] How do you HA your storage?

[Corey Kovacs]

What you seem to be describing is the mirror target for device mapper.

Another alternative would be to setup a software raid using multipath'd luns.

SANVOL1            SANVOL2
   |                           |
   \                          /
    \                       /
      \                   /
    MPATH1    MPATH2
         \             /
       RAID 1 DEV
               |
             PV
               |
              VG
               |
              LV

That might work

-C


On Sat, Apr 30, 2011 at 10:08 AM, urgrue <urgrue at bulbous.org> wrote:
> But, how do you get dm-multipath to consider two different LUNs to be in
> fact two paths to the same device?
> I mean, normally multipath has two paths to one device.
> When we're talking about san-level mirroring, we've got two paths to two
> different devices (which just happen to contain identical data).
>
> On 30/4/11 11:47, Kit Gerrits wrote:
>>
>> With dual-controller arrays, dm-multipath  keeps checking if the current
>> device is still responding and switches to a different path if it is not.
>> (for examply, by reading sector 0)
>>
>> With SAN failover, you may need to tell the secondary SAN LUN to go into
>> read-write mode.
>> Unfortunately, I am not familiar with tying this into RHEL.
>> (also, sector 0 will already be readable on the secundary LUN, but not
>> writable)
>>
>> Maybe there is a write test, which tries to write to both SANs
>> The one which allows write access will become the active LUN.
>>
>> If you can switch your SANs inside 30 seconds, you might even be able to
>> salvage/execute pending write operations.
>>
>>
>> Regards,
>>
>> Kit
>>
>> -----Original Message-----
>> From: linux-cluster-bounces at redhat.com
>> [mailto:linux-cluster-bounces at redhat.com] On Behalf Of urgrue
>> Sent: zaterdag 30 april 2011 11:01
>> To: linux-cluster at redhat.com
>> Subject: [Linux-cluster] How do you HA your storage?
>>
>> I'm struggling to find the best way to deal with SAN failover.
>> By this I mean the common scenario where you have SAN-based mirroring.
>> It's pretty easy with host-based mirroring (md, DRBD, LVM, etc) but how
>> can
>> you minimize the impact and manual effort to recover from losing a LUN,
>> and
>> needing to somehow get your system to realize the data is now on a
>> different
>> LUN (the now-active mirror)?
>> --
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