Setting Up Multipathing

If you choose to use it, set up multipathing before you install Adaptive Server.

There are several multipath applications are available. Native Linux device mapper multipath support (DM) has been added to the Linux 2.6 kernel tree with the release of 2.6.13, and has been backported into Red Hat Enterprise Linux 4 in Update 2 and into Novell SUSE Linux Enterprise Server 9 in Service Pack 2. To setup multipathing on Linux:

Edit the /etc/multipath.conf file by:
- Commenting out the following lines at the top of the file. This section of the configuration file, in its initial state, blacklists all devices. You must comment it out to enable multipathing:
```
blacklist {
      devnode "*"
}
```
- Adding configuration information. For example:
```
        multipath {
                wwid    360060e80056fb70000006fb700000816
                alias   TEST_DATA
                path_grouping_policy failover
                mode 660
                uid 8205
                gid 471
        }
```
Run these commands:
```
# modprobe dm-multipath – add multipathing module to Linux kernel
# modprobe dm-round-robin – add multipathing round-robin module to Linux kernel
# /etc/init.d/multipathd start – start multipath service
# multipath – automatically detect multiple paths to devices and configure multipathing
# chkconfig multipathd on – turn on multipath service
# multipath –l – displays all paths to devices
```
The /dev/mapper/mpathN devices are persistent and they are created early in the boot process. Therefore these are the device names that should be used to access the multipathed devices.
For example:
- /usr2/sybase/ASE1503/dev/wdb_data – is a symbolic link pointing to /dev/raw/raw73
  - /dev/raw/raw73 – is a raw character device mapped to /dev/mapper/mp_wdb_data
    /dev/mapper/mp_wdb_data – is a multipath device which contains two paths /dev/sdbf & /dev/sds.
    /dev/sdbf – is block device that corresponds to SCSI generic raw character device /dev/sg61
    
    /dev/sds – is block device that corresponds to SCSI generic raw character device /dev/sg20