Re: Is it safe to use the bigalloc feature in the case of ext4 filesystem?

[Mikhail Morfikov <mmorfikov@gmail.com>]

On 29/07/2021 19.59, Theodore Ts'o wrote:
> On Wed, Jul 28, 2021 at 11:36:27AM +0200, Mikhail Morfikov wrote:
>> Thanks for the answer.
>>
>> I have one question. Basically there's the /etc/mke2fs.conf file and 
>> I've created the following stanza in it:
>>
>> bigdata = {
>>                 errors = remount-ro
>>                 features = has_journal,extent,huge_file,flex_bg,metadata_csum,64bit,dir_nlink,extra_isize,bigalloc,^uninit_bg,sparse_super2
>>                 inode_size = 256
>>                 inode_ratio = 4194304
>>                 cluster_size = 4M
>>                 reserved_ratio = 0
>>                 lazy_itable_init = 0
>>                 lazy_journal_init = 0
>>         }
>>
>> It looks like the cluster_size parameter is ignored in such case (I've 
>> tried both 4M and 4194304 values), and the filesystem was created with 
>> 64K cluster size (via mkfs -t bigdata -L bigdata /dev/sdb1 ), which is 
>> the default when the bigalloc feature is set.
> 
> It does work, but you need to use an integer value for cluster_size,
> and it needs to be in the [fs_types[ section.  So something like what I
> have attached below.
> 
> And then try using the command "mke2fs -t ext4 -T bigdata -L bigdata
> /dev/sdb1".

Yes, this helped and the cluster size was set to 4194304 as it should.

> 
> 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.

I'll try them both and see whether I could use either one of them on 
my drive.

> 
> Cheers,
> 
> 						- Ted
> 
> [defaults]
> 	base_features = sparse_super,large_file,filetype,resize_inode,dir_index,ext_attr
> 	default_mntopts = acl,user_xattr
> 	enable_periodic_fsck = 0
> 	blocksize = 4096
> 	inode_size = 256
> 	inode_ratio = 16384
> 	undo_dir = /var/lib/e2fsprogs/undo
> 
> [fs_types]
> 	ext3 = {
> 		features = has_journal
> 	}
> 	ext4 = {
> 		features = has_journal,extent,huge_file,flex_bg,metadata_csum,64bit,dir_nlink,extra_isize
> 		inode_size = 256
> 	}
> 	small = {
> 		blocksize = 1024
> 		inode_size = 128
> 		inode_ratio = 4096
> 	}
> 	floppy = {
> 		blocksize = 1024
> 		inode_size = 128
> 		inode_ratio = 8192
> 	}
> 	big = {
> 		inode_ratio = 32768
> 	}
> 	huge = {
> 		inode_ratio = 65536
> 	}
> 	news = {
> 		inode_ratio = 4096
> 	}
> 	largefile = {
> 		inode_ratio = 1048576
> 		blocksize = -1
> 	}
> 	largefile4 = {
> 		inode_ratio = 4194304
> 		blocksize = -1
> 	}
> 	hurd = {
> 	     blocksize = 4096
> 	     inode_size = 128
> 	}
> 	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
> 	}
> 	bigdata = {
> 		errors = remount-ro
> 		features = has_journal,extent,huge_file,flex_bg,metadata_csum,64bit,dir_nlink,extra_isize,bigalloc,^uninit_bg,sparse_super2
> 		inode_size = 256
> 		inode_ratio = 4194304
> 		cluster_size = 4194304
> 		reserved_ratio = 0
> 		lazy_itable_init = 0
> 		lazy_journal_init = 0
> 	}
>