- Red Hat Enterprise Linux (RHEL)
- Linux DM Multipath (
- Additional path aggregation solution(s)
- Does Red Hat support or recommend running two multipath solutions at the same time?
- Is it possible or advisable to use more than one path aggregation software at once?
- Can I use Linux DM Multipath (
device-mapper-multipath) at the same time as EMC PowerPath, Veritas Dynamic Multi-Pathing (
DMP), IBM Subsystem Device Driver (
SDD), Fujitsu Eternus, Hitachi Dynamic Link Manager (
HDLM), Huawei UltraPath (updisk, up_adapter), and so on?
- Red Hat works with numerous hardware vendors to qualify and provide full support for DM Multipath (device-mapper-multipath) for path aggregation on Red Hat Enterprise Linux.
- It is possible to run other third-party path aggregation solutions concurrently on a system with DM Multipath. If this is done, the following restrictions must be observed:
- The third-party vendor also agrees to support systems that are configured in this manner. Customers are encouraged to contact third-party vendors regarding their support statements and requirements in the use of concurrent multipath solutions.
- The third-party vendor must ensure that its multipath solution will only control the devices that are allocated to it, and will not interfere with other devices that are outside its control. These devices may be under the control to other multipath solutions.
- It is understood that the usual policy with regard to support for systems with third-party software installed applies. That is, when a problem occurs, and it is feasible to remove the third-party software for troubleshooting, Red Hat may request that this be done. If the the third-party software can not be removed for troubleshooting, Red Hat will undertake a commercially reasonable effort to address the problem, and will use its partner contacts, or TSANet, to collaborate with vendors on shared customer issues. Refer to: https://access.redhat.com/site/articles/1067.
- On-line storage reconfiguration is not recommended on RHEL 4 and RHEL 5 systems when there are multiple path aggregation solutions running concurrently. The system should be brought down when storage devices are added, removed, or reconfigured, and then rebooted. This is a precaution, to avoid possible problems related to device scanning, discovery, mutual exclusion, and the assembly of logical devices (md and LVM). These potential problems are resolved in RHEL 6 with the more complete integration with udev.
The concurrent use of multiple path aggregation solutions on a system presents a number of challenges. A method of mutual exclusion must be ensured, yet some interaction is typically unavoidable because of the need for each implementation to scan devices at start-up. Next, the order of events at start-up including discovery, module load, udev scanning, device-mapper, md and LVM device aggregation, mount, etc., is critical, and has presented difficulty in the past. As a result of this complexity, on-line reconfiguration of systems that have multiple path aggregation solutions is not recommended on RHEL 4 and 5 systems. Finally, path aggregation solutions typically involve closed-source kernel modules that Red Hat can not review, test, or debug. This risk must be addressed by the third-party vendor.
Red Hat works with its partners to test device-mapper-multipath on a wide variety of hardware devices. Red Hat does not test third-party multipath software. If these products will be used, the third-party provider must take responsibility for this testing and support. If the third-party vendor provides this support, then Red Hat will provide a commercially reasonable effort to support systems that run these third-party products, whether they are run alone or concurrently with device-mapper-multipath.
- Red Hat Enterprise Linux
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