Administrator Guide

Live Volume with Linux/UNIX
86 Dell EMC SC Series: Synchronous Replication and Live Volume | CML1064
• While device path_selector policies service-time and round-robin are supported by DM-Multipath,
Dell Technologies has performed extensive testing with round-robin policy only. See Figure 65.
• In a uniform configuration where primary and secondary paths are mapped to the Linux host, these
paths are grouped into a single group and the round-robin policy spreads I/O to these paths with
equal weight even though the secondary paths might have higher latency. This is because I/O issued
to the secondary paths is proxied through the replication link to the primary SC Series array as
described in section 5.2. Hence, the overall application performance would be limited by the slowest
paths.
10.5 Live Volume with ALUA
SCOS 7.3 enhances Live Volume with the introduction of the ALUA capability. ALUA-optimized Live Volumes
report the preferred storage access paths to the host by indicating which paths are optimized and non-
optimized. In a uniform configuration, paths from the primary Live Volume are seen as optimized, while paths
from the secondary Live Volume are seen as non-optimized. With proper configuration in the host's MPIO
software, the host can direct I/O only to the optimized storage paths, improving the overall I/O latency and
performance by avoiding sending I/O through the slower paths.
Note: As of SCOS 7.3, the ALUA optimization feature has not been fully tested on the Linux platform.
Therefore, it is not recommended to enable the feature.
10.5.1 Disable ALUA prioritization in DM-Multipath configuration
For reasons mentioned in the previous section, DM-Multipath ALUA settings should be avoided as of SCOS
7.3. Therefore, do not set prio alua for COMPELNT devices in the /etc/multipath.conf file. Rather, use prio
const in the COMPELNT device stanza as shown in 10.4.1.