I have a question concerning the *hugefiles* parameters. When a 
filesystems is created using the hugefiles stanza, it also creates 
lots of chunk-* files inside of the /storage/ dir. You say that it 
guarantees the huge files to be 100% contiguous. But if I create 
the filesystem with the preallocated files that consume the whole 
drive, how am I suppose to use that drive? :) Are the files only
temporary, and should they be removed once the filesystem is 
"ready"? What's the purpose of such options? Do they affect the 
EXT4 metadata in some way? I mean, what's the change compared to 
not using the options?

Also I have a question concerning the hugefiles stanza 
itself -- it's missing the bigalloc feature, should it be there?


On 29/07/2021 19.59, Theodore Ts'o wrote:

...
If you see the hugefile and hugefiles stanzas below, that's an example
of one way bigalloc has gotten a fair amount of use.  In this use case
mke2fs has pre-allocated the huge data files guaranteeing that they
will be 100% contiguous.  We're using a 32k cluster becuase there are
some metadata files where better allocation efficiencies is desired.

...

	hugefiles = {
		features = extent,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize,^resize_inode,sparse_super2
		hash_alg = half_md4
		reserved_ratio = 0.0
		num_backup_sb = 0
		packed_meta_blocks = 1
		make_hugefiles = 1
		inode_ratio = 4194304
		hugefiles_dir = /storage
		hugefiles_name = chunk-
		hugefiles_digits = 5
		hugefiles_size = 4G
		hugefiles_align = 256M
		hugefiles_align_disk = true
		zero_hugefiles = false
		flex_bg_size = 262144
	}

	hugefile = {
		features = extent,huge_file,bigalloc,flex_bg,uninit_bg,dir_nlink,extra_isize,^resize_inode,sparse_super2
		cluster_size = 32768
		hash_alg = half_md4
		reserved_ratio = 0.0
		num_backup_sb = 0
		packed_meta_blocks = 1
		make_hugefiles = 1
		inode_ratio = 4194304
		hugefiles_dir = /storage
		hugefiles_name = huge-file
		hugefiles_digits = 0
		hugefiles_size = 0
		hugefiles_align = 256M
		hugefiles_align_disk = true
		num_hugefiles = 1
		zero_hugefiles = false
	}