[LU-9489] PFL layout uses full xattr space even when not init

• Type: Task
• Resolution: Fixed
• Priority: Blocker
• Fix Version/s: Lustre 2.10.0
• Affects Version/s: Lustre 2.10.0
• Assignee: Zhenyu Xu
• Reporter: Andreas Dilger

Description

While testing lfs find I noticed that the size of the components (lcme_size) is based on the instantiated size and not the size of only the component header and the layout template. Creating an empty file and then writing to the file to instantiste all of the components does not change the lcme_size.

If the on-disk xattr is reserving all the space for the instantiated component, then this is losing one of the major benefits of PFL. On a large system with hundreds of OSTs, if the last component (typically "-c -1") the uninstantiated last component will need multiple KB of space in the xattr, and this will not fit into the inode. Then, all inodes will have an external xattr block, instead of only the large files that need the wide striping, and this will significantly impact small file performance.

Issue Links

• is related to: LU-9349 PFL known issues tracking ticket