Multipath Configuration

If your storage system has multi-path capable (dual ported) SAS media connected via a SAS JBOD or internal SAS expander QuantaStor will try to automatically enable multipath support for your devices. Multipath devices appear in the system with the dm-uuid-mpath prefix. Multipathing improves redundancy, fault-tolerance and in some cases improves performance.

Multi-path Configuration with RAID Controllers

If you are using a RAID controller it will internally manage the multiple paths to the device automatically so there is no additional configuration required except to make sure that you have two cables connecting the controller to the SAS expander.

Multi-path Configuration with HBAs

For systems with SAS HBAs there are some additional steps required to setup the QuantaStor system for multipath access. Specifically, you must add entries to the /etc/multipath.conf file then restart the multipath services.

Configuring the /etc/multipath.conf File

QuantaStor is Linux based and uses the DMMP (Device Mapper Multi-Path) driver to manage multipathing. The multipath service can be restarted at any time at the command line using the command 'service multipath-tools restart'. Configuration of this service is managed via the configuration file located at /etc/multipath.conf which contains a set of rules indicating which devices (identified by Vendor / Model) should be managed by the multipath service and which should be ignored. The base configuration is setup so that no multipath management is done for SAS devices as this is the most common and simplest configuration mode. To enable multipath management you must add a section to the 'blacklist_exceptions' area of the file indicating the vendor and model of your SAS devices. The vendor model information for your SAS devices can be found using this command 'grep Vendor /proc/scsi/scsi'. To summarize:

• grep Vendor /proc/scsi/scsi
  • Returns the vendor / model information for your SAS devices
• nano /etc/multipath.conf
  • Add a section to the blacklist_exceptions area for your SAS device, example (note the use of a wildcard '*') :

   device {
           vendor "SEAGATE"
           model "ST33000*"
   }

• service multipath-tools restart
  • Restarts the multipath service
• multipath -ll
  • Shows your devices with multiple paths to them

Pool Configuration

Once all the above is done you'll need to go into the QuantaStor web management interface and choose 'Scan for Disks' to make the new device mapper paths appear. If you have already created a storage pool using standard paths rather than the /dev/mapper/mpath* paths then you'll need to run a zpool export/import operation to re-import the pool using the device mapper paths. To do this you will need to first do a 'Stop Storage Pool' then at the command line / console you'll need to run these commands:

• zpool export qs-POOLID
• zpool import -d /dev/mapper qs-POOLID

Note that you must replace qs-POOLID with the actual ID of the storage pool. You can also get this ID by running the 'zpool status' command.

Troubleshooting Multipath Configurations

• Only Single Path
  • If you only see one path to your device but the multipath driver is recognizing your device by displaying it in the output of 'multipath -ll' then you may have a cabling problem that is only providing the system with a single path to the device.
• No Paths Appear
  • If you don't see any devices in the output of 'multipath -ll' then there's probably something wrong with the device entry you added to the multipath.conf file into the blacklist_exceptions for your particular vendor/model of SAS device. Double check the output from 'cat /proc/scsi/scsi' to make sure that you have a correct rule added to the multipath.conf file.