On 01/22/2016 02:31 PM, Ravikanth Nalla wrote: > v2: > - changes merged with latest mainline and functionality re-verified. > - performed additional tests to illustrate performance benefits of > using this feature in certain configuration. > > In a dm multipath environment, providing end user with an option of > selecting preferred path for an I/O in the SAN based on path speed, > health status and user preference is found to be useful. This allows > a user to select a reliable path over flakey/bad paths thereby > achieving higher I/O success rate. The specific scenario in which > it is found to be useful is where a user has a need to eliminate > the paths experiencing frequent I/O errors due to SAN failures and > use the best performing path for I/O whenever it is available. > > Another scenario where it is found to be useful is in providing > option for user to select a high speed path (say 16GB/8GB FC) > over alternative low speed paths (4GB/2GB FC). > > A new dm path selector kernel loadable module named "dm_pref_path" > is introduced to handle preferred path load balance policy > (pref-path) operations. The key operations of this policy is to > select and return user specified path from the current discovered > online/ healthy paths. If the user specified path do not exist in > the online/ healthy paths list due to path being currently in > failed state or user has mentioned wrong device information, it > will fall back to round-robin policy, where all the online/ healthy > paths are given equal preference. > > Functionality provided in this module is verified on wide variety > of servers ( with 2 CPU sockets, 4 CPU sockets and 8 CPU sockets). > Additionally in some specific multipathing configurations involving > varied path speeds, proposed preferred path policy provided some > performance improvements over existing round-robin and service-time > load balance policies. > Shouldn't service-time provide similar functionality? After all, for all scenarios described above the preferred path would have a lower service time, so they should be selected automatically, no? Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
