[LU-13564] WBC: inode and space grant mechanism under WBC

• Type: Technical task
• Resolution: Unresolved
• Priority: Minor
• Assignee: WC Triage
• Reporter: Qian Yingjin

Description

Under WBC, all metadata and data are cached in MemFS, not being flushed to MDT and OSTs. To void running out of the server space, it needs to design a grant mechanism similar to current OST space grant to control inodes grant from MDT.
The following points need to consider for grant mechanism under WBC:

• In the DNE environment, how to select MDT for the newly creation? Maybe the whole root WBC subtree should be located on the same MDT?
• In current WBC implementation, the data objects for the regular file will be created when flush the file to MDT and the layout will be instantiated also. This can be optimized as follows:
  • It could send the current size of the file to MDT, then it can determine how to allocate data object more clear accordingly.
  • Delay to allocate data objects and instantiate the layout for the regular file unless it is necessary.