dual HBA SAN attached + raid + LVM

Steve Mickeler steve at neptune.ca
Wed Aug 21 17:41:00 CDT 2002


The raid multipath is an option in the 2.4 kernels.

CONFIG_MD_MULTIPATH
  Multipath-IO is the ability of certain devices to address the same
  physical disk over multiple 'IO paths'. The code ensures that such
  paths can be defined and handled at runtime, and ensures that a
  transparent failover to the backup path(s) happens if a IO errors
  arrives on the primary path.

So, if you have 2 paths to a single disk via seperate
controllers you would you would setup your /etc/raidtab entry to look
something like this:

raiddev /dev/md0
        raid-level      multipath
        nr-raid-disks   2

device                  /dev/sdw1
raid-disk               1

device                  /dev/sdbm1
raid-disk               0

Now /dev/md0 is the multipathed metadevice.

I was able to create these devices but mke2fs would hang when I tried to
put a filesystem on the metadevice.

Doing some google searching found that there are some "issues" with fibre
channel and raid multipath.

LVM would also seg fault when the system rebooted and it ran a vgscan and
saw the same LVM data via 2 volumes.

So far the only way I have gotten this box to be stable and SAN attached
is to have only 1 connection to the SAN.

Cheers.

> > Linux raid multipath devices setup to create a single metadevice via the 2
> > paths back to the same disk.
>
> can you elaborate ? what linux raid multipath devices are you referring to ?
>
> > I currently have all the hardware to do this but ran into a few snags that
> > have left me only reliably running with 1 HBA attached to the SAN.
>
> the lack of powerpath/dmp/atf ?
>
>
> regards,
>
> -jason
>
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[-] Steve Mickeler [ steve at neptune.ca ]

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