Linux Blue

bigalloc (1)

linux-3.2でkernelにマージされたbigallocについて

デフォルトでは有効にならないため、"-O bigalloc"でext4のbigallocが有効になる(e2fsprogsはcommit: c6ed60cdeb1 以降。その後バグ修正も色々入っているので最新のを利用したほうがよい)。
また、-C でcluster(ブロックの集まり)のサイズを指定できる。デフォルトは16K(4KB*16)。

# ./mke2fs -t ext4 -O bigalloc /dev/sda8
mke2fs 1.42 (29-Nov-2011)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Cluster size=65536 (log=6)
Stride=0 blocks, Stripe width=0 blocks
129664 inodes, 2074112 blocks
103705 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=2147483648
4 block groups
524288 blocks per group, 32768 clusters per group
32416 inodes per group
Superblock backups stored on blocks:
524288, 1572864

Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

debugfsでbigallocが設定されていることを確認

# ./debugfs -R stats /dev/sda8
debugfs 1.42 (29-Nov-2011)

Filesystem volume name:
Last mounted on:
Filesystem UUID: 5c8b5f8e-5059-4215-aa8e-24a930c8ce92
Filesystem magic number: 0xEF53
Filesystem revision #: 1 (dynamic)
Filesystem features: has_journal ext_attr resize_inode dir_index filetype extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize bigalloc
Filesystem flags: signed_directory_hash
Default mount options: user_xattr acl
Filesystem state: clean
Errors behavior: Continue
Filesystem OS type: Linux
Inode count: 129664
Block count: 2074112
Reserved block count: 103705
Free blocks: 2033024
Free inodes: 129653
First block: 0
Block size: 4096
Cluster size: 65536
Reserved GDT blocks: 31
Blocks per group: 524288
Clusters per group: 32768
Inodes per group: 32416
Inode blocks per group: 2026
Flex block group size: 16
Filesystem created: Sat Feb 11 22:28:11 2012
Last mount time: n/a
Last write time: Sat Feb 11 22:28:11 2012
Mount count: 0
Maximum mount count: -1
Last checked: Sat Feb 11 22:28:11 2012
Check interval: 0 ()
Lifetime writes: 128 MB
Reserved blocks uid: 0 (user root)
Reserved blocks gid: 0 (group root)
First inode: 11
Inode size: 256
Required extra isize: 28
Desired extra isize: 28
Journal inode: 8
Default directory hash: half_md4
Directory Hash Seed: f7ac2cd7-ee6a-43d2-b8ef-de2533eb8008
Journal backup: inode blocks
Directories: 2
Group 0: block bitmap at 33, inode bitmap at 49, inode table at 65
32254 free clusters, 32405 free inodes, 2 used directories, 32405 unused inodes
...

bigallocの詳細はまた今度