[LU-15002] Allocate metagroup descriptors continuously if possible

• Type: Improvement
• Resolution: Fixed
• Priority: Major
• Fix Version/s: Lustre 2.16.0

Epic/Theme

ldiskfs

• Assignee: Dongyang Li
• Reporter: Artem Blagodarenko (Inactive)

Description

If LDISKFS target formatted with meta_bg option, then group descriptors are split across a target. Pre-reading optimization doesn't work for such metadata.

With the current cluster size (no bigalloc option) a partition >256TB can not be created without meta_bg, but there is a workaround.

Filesystems can either be created using this new block group descriptor layout, or existing filesystems can be resized online, and the field s_first_meta_bg in the superblock will indicate the first block group using this new layout.

The next steps allow to the creation of continuous group descriptors for the first 256TB and use meta_bg for all other groups.

      1. Create < 256 TB partition without the meta_bg flag

      2. Extend the partition to the whole disk

These steps can be done manually or mkfs can be modified.

Issue Links

• is related to: LU-16750 optimize ldiskfs internal metadata allocation for hybrid storage LUNs