Does ZFS currently attempt to group metadata in large sector-ranges on the disk? Can this be expected to happen "automagically" - i.e. during each TXG close we have to COW-update whole branches of the blockpointer tree, so these new blocks might "just happen" to always coalesce into larger sector groups?
Rationale: larger regions dedicated to smallish block pointers might be better cached (i.e. with VDEV prefetch) and speed up housekeeping including scrubs and zfs sends. They could also reduce fragmentation of "bulk" userdata stored in larger blocks. These could also prove useful to implement my "Feature #1044: ZFS: Allow specifying minimum dataset/metaslab block size AND alignment" posted in https://www.illumos.org/issues/1044 Industry examples of grouped metadata could include copies of the FAT table in FAT/pcfs, and the $MFT pseudofile on NTFS. Difference is that ZFS metadata size is dynamic, so metadata regions should not rely on any predefined sizes. If this feature is not yet present, is it difficult or unreasonable for some reason to add one? Thanks, //Jim _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
