ASM Disk Resync Takes Long Time After Disk Online
Last updated on JUNE 16, 2016
Applies to:Oracle Database - Enterprise Edition - Version 18.104.22.168 to 22.214.171.124 [Release 12.1]
Information in this document applies to any platform.
ASM disk resync takes long time after disk online. ASM resync delay. ASM resync performance degradation in 12c.
The ASM resync (also known as the fast mirror resync) may take a very long time in ASM version 12c. This may be especially pronounced in Exadata with the large grid disks and lot of data in the disk group.
When ASM disks are brought online, e.g. in Exadata by running the following command on the storage cell "cellcli -e alter griddisk all active", there might be a significant delay (potentially hours) in staring the actual resync work. On that storage cell, the output of "cellcli -e list griddisk attributes name,status,asmmodestatus" would show the ASMMODESTATUS in state SYNCH for a very long time.
On the database server, there would be no sign of activity in ASM ARB0 process in any of the ASM instances. The pstack of the XDWK process, in the ASM instance performing the resync, would show the following (note the kfrSyncLog and kfrSyncToAba on the stack):
Note that once the resync completed, there was the disk group rebalance. In version 12c it is normal and expected for the rebalance to run after the resync operation.
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