DCM logging in DCO与DCM logging using DCM log plexes的对比

从InfoScale 7.4.2版本开始，VVR支持DCM logging in DCO。

以下是关于DCM logging in DCO与DCM logging using DCM log plexes的对比。

DCM logging using DCM log plexes面临的一些问题
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• In FSS-CVR environment
– Allocation constraints such as mirror=host are not followed for DCM log plexes, unlike other data plexes of data volume, compromising overall data resiliency for DCM.
– Fixed number of DCM plexes are added to data volume, irrespective of number of mirrors data volume has, impacting the availability of DCM.

• Application IO tracking happens at multiple places in cases having data volumes with detached objects/snapshots associated, along with DCM in active state, leading to performance impact during this window.

• Data volume resize does not resize corresponding DCM log associated.
– Smaller size DCM leads to larger region size for tracking application IOs
– Due to size limitations, DCM sync operation does not use SmartMove feature and performs full sync, impacting overall sync performance.

• In EC-VVR environment, DCM log plexes need to be handled (removed and added back) explicitly during rebalance or re-layout operations.

DCM logging in DCO的增强
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• In FSS-CVR environment, DCM log follows same failure domain as corresponding data volume, with DCM availability remaining un-compromised with respect to corresponding data volume availability.
– In Non FSS environment, minimum DCM availability is maintained by allocating 2 copies of log.

• Improve overall application IO performance, for data volumes associated with detached objects/snapshots, and DCM in active state, by tracking IOs at single point i.e. DRL inside DCO object.

• Maintain DCM log size in proportion with corresponding data volume size, to track IOs finer grain with optimal region size and integrate well with SmartMove feature for large size data volumes.

• Co-existence with other features and the operations such as EC relayout/rebalance without any explicit handling.
 

InfoScale7.4.2 Replication Administrator's Guide关于 DCM logging in DCO 的说明
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In InfoScale 7.4.1 and earlier releases, when replication is configured, the DCM log is associated as a separate log plex to each data volume in the RVG. Starting with InfoScale 7.4.2, DCM logs are allocated as per-volume FMR maps in DCO for new replication setups, by default. However, you can also choose to configure DCM log plexes for the new replication setups.

When the DCM logs are configured in DCO:

• DCM follows the same resiliency and availability constraints as that of the data volume. As a result, in FSS-CVR environments, the availability and resiliency for DCM is not compromised.
• DCM log size is maintained in proportion to the corresponding data volume size during the resize operation. This leads to efficient IO tracking and also works well with SmartMove feature for large size data volumes.

The DCM logging in DCO is enabled at the RVG level and is thus enabled for all the data volumes under that RVG. To enable support for DCM logging in DCO, the disk group version must be 290 or later.

Note: InfoScale does not allow the use of different DCM logging types under the same RVG.