红帽全球峰会第 1 章 Overview of device mapper multipathing
DM Multipath provides redundancy through failover in active/passive configurations and improved performance by spreading I/O across multiple paths in active/active mode.
DM Multipath provides:
- Redundancy
DM Multipath can provide failover in an active/passive configuration. In an active/passive configuration, only a subset of the paths is used at any time for I/O. If any element of an I/O path such as the cable, switch, or controller fails, DM Multipath switches to an alternate path. For more information, see:
-
multipath(8)andmultipathd(8)man pages on your system -
/etc/multipath.conffile
-
The number of paths is dependent on the setup. Usually, DM Multipath setups have 2, 4, or 8 paths to the storage, but this is a common setup and other numbers are possible for the paths.
- Improved Performance
- DM Multipath can be configured in an active/active mode, where I/O is spread over the paths in a round-robin fashion. In some configurations, DM Multipath can detect loading on the I/O paths and dynamically rebalance the load.
Active/passive configuration provides redundant I/O paths through dual HBAs and SAN switches to a single RAID device, enabling automatic failover when path components fail.
In this configuration, there are two Host Bus Adapters (HBAs) on the server, two SAN switches, and two RAID controllers. Following are the possible failure in this configuration:
- HBA failure
- Fibre Channel cable failure
- SAN switch failure
- Array controller port failure
With DM Multipath configured, a failure at any of these points causes DM Multipath to switch to the alternate I/O path. The following image describes the configuration with two I/O paths from the server to a RAID device. Here, there is one I/O path that goes through hba1, SAN1, and cntrlr1 and a second I/O path that goes through hba2, SAN2, and cntrlr2.
图 1.1. Active/Passive multipath configuration with one RAID device
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