Understanding whether the FlexVol volumes associated with an aggregate are eligible for write caching can help you ensure that the volumes with high performance requirements can get the maximum performance improvement from having their associated aggregate converted to a Flash Pool aggregate.
You can use this procedure to determine write caching eligibility to help you decide which aggregates are good candidates to become Flash Pool aggregates. You do not need any SSDs to complete this procedure.
Flash Pool aggregates employ two types of caching: read caching and write caching. Read caching is available for all volumes. Write caching is usually available for most volumes, but might be disabled due to the following reasons:
The error message for this condition refers to an incompatible file system version.
The error message for this condition says that one or more volumes in the aggregate is not eligible for write caching.
If the aggregate you want to convert to a Flash Pool aggregate was created using Data ONTAP 7.1 or earlier and you want write caching to be enabled for its associated volumes, you must copy each FlexVol volume associated with the aggregate to a new aggregate and convert the new aggregate to a Flash Pool aggregate. If some volumes are ineligible due to an ID collision, you can resolve the ID collision by moving the ineligible volumes to another aggregate (and back again if needed) or simply proceed with the conversion, using the force option. In this case, the ineligible volumes do not benefit from the Flash Pool aggregate cache for write operations.
|Flash Pool aggregate capability is successfully enabled||Disable the Flash Pool aggregate capability again: aggr options aggr_name hybrid_enabled false
You have completed this task. All of the volumes associated with the aggregate are eligible for write caching.
|Command displays an error message telling you that the aggregate cannot be converted to a Flash Pool aggregate||Go to the next step.|
|If the volumes are ineligible because...||Then...|
|The aggregate was created using Data ONTAP 7.1 or earlier, and you do not need to enable write caching for its associated volumes||You can convert the aggregate by using the force option.|
|The aggregate was created using Data ONTAP 7.1 or earlier, and you want to enable write caching for its associated volumes||Copy all of the volumes associated with this aggregate to a new aggregate, and then repeat this procedure on the new aggregate.|
|There are ID collisions for some volumes in the aggregate, and you do not need to enable write caching for those volumes||You can convert the aggregate by using the force option.|
|There are ID collisions for some volumes in the aggregate, and you need to enable write caching for those volumes||Complete the following steps:
The following example shows the system output when volumes within the aggregate have ID collisions:
sys1> aggr options aggr1 hybrid_enabled on aggr options: Failed to set caching policies on Aggregate "aggr1" because one or more volumes in the aggregate is not eligible for write caching. sys1> vol status -v vol8 ........... svo_allow_rman=off, svo_reject_errors=off, no_i2p=off, fractional_reserve=100, extent=off, try_first=volume_grow, read_realloc=off, snapshot_clone_dependency=off, no_delete_log=off, dlog_hole_reserve=off, nbu_archival_snap=off Volume has clones: vol8_clone Volume UUID: 4a7afb51-47cd-11e1-bebd-123478563412 Containing aggregate: 'aggr1' Volinfo mode: 7-mode Volume Instance UUID: 4a7afb94-47cd-11e1-bebd-123478563412 Volume Provenance UUID: 4a7afb94-47cd-11e1-bebd-123478563412 Plex /aggr1/plex0: online, normal, active RAID group /aggr1/plex0/rg0: normal, block checksums RAID group /aggr1/plex0/rg1: normal, block checksums Snapshot autodelete settings for vol8: state=off commitment=try trigger=volume target_free_space=20% delete_order=oldest_first defer_delete=user_created prefix=(not specified) destroy_list=none Volume autosize settings: state=off Hybrid Cache: Eligibility=read Write caching ineligibility reason=ID Collision(25443)