Creating & converting ext2 3 4

ext2, ext3, ext4 filesystems creation on Linux Ext2, ext3 and ex4 are most popular file systems on Linux, Ext2 was introduced in 1993 and was the first default file system in several linux distro like RedHat, Debian etc.. Here few examples show you how to create these filesystems. Spearate journal and data on different device In most of cases, and it is default, the journal(if there is) and data device are on the same block device. Seperate journal and data brings performance improvement, on the other hand, introduce the management complexity and the chance of data inconsistency risk. Prepare block device You can use a whole disk/lun for a filesystem, or partition it into different partitions by fdisk or parted Create ext2 filesystem     Maximum file size is 16GB – 2TB.     Journaling feature is not available. You can use any one of the command to create an ext2 filesystem #mkfs -L <volume-label> -t ext2 /dev/sdxx #mkfs.ext2 -L <volume-label> /dev/sdxx #mke2fs -L <volume-label> -t ext2 /dev/sdxx -t stands for filesystem type, default is ext2 -L stands for filesystem volume label Create ext3 filesystem     Ext3 file system was introduced in 2001 and same was integrated in Kernel 2.4.15 with journaling feature, which is to improve reliability and eliminates need to check file system after unclean shutdown.     Max file size 16GB – 2TB.     Provide facility to upgrade from Ext2 to Ext3 file systems without having to back up and restore data. #mkfs -L <volume-label> -t ext3 /dev/sdxx #mkfs.ext3 -L <volume-label> /dev/sdxx #mke2fs -L <volume-label> -t ext3 /dev/sdxx #mke2fs -L <volume-label> -j /dev/sdxx -t stands for filesystem type, default is ext2 -L stands for filesystem volume label -j stands for journal(as if using -t ext3 ) Created ext4 filesystem     On October 2008, Ext4 as stable code were merged in the Kernel 2.6.28 which contains Ext4 file system.     Backward compatibility.     Max file size 16GB to 16TB.     Ext4 file system have option to Turn Off journaling feature.     Other features like Sub Directory Scalability, Multiblock Allocation, Delayed Allocation, Fast FSCK etc. #mkfs -L <volumelabel> -t ext4 /dev/sdxx #mke2fs -L <volume-label> -t ext4 /dev/sdxx #mkfs.ext4 -L <volume-label> /dev/sdxx Check a filesystem type To tell a filesystem type, simply run # df -T Filesystem           Type  1K-blocks    Used Available Use% Mounted on /dev/sda2            ext4    1477292  391364   1009220  28% / tmpfs                tmpfs   4030604   44456   3986148   2% /dev/shm /dev/sda1            ext4     197157   59247    127519  32% /boot /dev/mapper/vg0-home ext4   50281156 5702696  42017644  12% /home /dev/mapper/vg0-opt  ext4     999320    2152    944740   1% /opt /dev/mapper/vg0-tmp  ext4     499656     460    472984   1% /tmp /dev/mapper/vg0-usr  ext4    3966144 3058724    702620  82% /usr /dev/mapper/vg0-var  ext4    9964080  369196   9082068   4% /var To list specific filesystem mounted, simply run # df -t tmpfs Filesystem     1K-blocks  Used Available Use% Mounted on tmpfs            4030604 44456   3986148   2% /dev/shm Utility tune2fs offers more options to let you display, set filesystem parameters

Convert ext2 to ext3, ext4 Can they be converted to each other ? answer is yes Generally speaking, file system is divided into two segments called User Data and Metadata, luckily so far ext filesystems are made backward compatibility, so that they can be converted to each others. Before start convertion Convertion between ext2 to ext3, ext2 to ext4 can be done on the fly, however, it is always better to unmount file system and convert. I got into trouble once when converting ext2 to ext4, not a big deal, fixed by fsck. All conversion can be done by utility tune2fs Supported convertion: Ext2 --> Ext3 Ext3 --> Ext2 Ext2 --> Ext4 Ext3 --> Ext4 Note: Ext4 to Ext2/3 convertion is kind of possible, but not supported and recommded. Create an ext2 file system # mkfs -L testfs -t ext2 /dev/mapper/vg0-lvol0 mke2fs 1.41.12 (17-May-2010) Filesystem label=testfs OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) Stride=0 blocks, Stripe width=0 blocks 655360 inodes, 2621440 blocks 131072 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=2684354560 80 block groups 32768 blocks per group, 32768 fragments per group 8192 inodes per group Superblock backups stored on blocks:     32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632 Writing inode tables: done                           Writing superblocks and filesystem accounting information: done This filesystem will be automatically checked every 32 mounts or 180 days, whichever comes first.  Use tune2fs -c or -i to override. And, I saved a filesystem parameter list for this ext2 filesystem #tune2fs -l /dev/mapper/vg0-lvol0 >ext2.parameters Convert Ext2 to Ext3 Change an ext2 file system to ext3 by enabling the journal feature # tune2fs -j /dev/mapper/vg0-lvol0 tune2fs 1.41.12 (17-May-2010) Creating journal inode: done This filesystem will be automatically checked every 32 mounts or 180 days, whichever comes first.  Use tune2fs -c or -i to override. What has been change? # diff ext2.parameters ext3.parameters < Filesystem features:      ext_attr resize_inode dir_index filetype sparse_super large_file > Filesystem features:      has_journal ext_attr resize_inode dir_index filetype sparse_super large_file < Free blocks:              2574545 > Free blocks:              2541744 > Journal inode:            8 > Journal backup:           inode blocks Note: I excluded timestamp different Convert Ext3 to Ext2 Just remove the journal  # tune2fs -O ^has_journal /dev/mapper/vg0-lvol0 tune2fs 1.41.12 (17-May-2010) Converting Ext2 to Ext4 Change an ext2 to ext4 file system by enabling the latest journaling feature. Run the following command. # tune2fs -O dir_index,has_journal,uninit_bg /dev/mapper/vg0-lvol0 tune2fs 1.41.12 (17-May-2010) Please run e2fsck on the filesystem. After running this command we MUST run fsck to fix up some on-disk structures that tune2fs has modified. # e2fsck /dev/mapper/vg0-lvol0 e2fsck 1.41.12 (17-May-2010) One or more block group descriptor checksums are invalid.  Fix<y>? yes Group descriptor 0 checksum is invalid.  FIXED. ... Group descriptor 79 checksum is invalid.  FIXED. testfs contains a file system with errors, check forced. Pass 1: Checking inodes, blocks, and sizes Pass 2: Checking directory structure Pass 3: Checking directory connectivity Pass 4: Checking reference counts Pass 5: Checking group summary information testfs: 11/655360 files (0.0% non-contiguous), 79696/2621440 blocks # tune2fs -O dir_index,has_journal,uninit_bg /dev/hdXX After convertion, see the parameters changes # diff ext2.parameters ext4.parameters < Filesystem features:      ext_attr resize_inode dir_index filetype sparse_super large_file > Filesystem features:      has_journal ext_attr resize_inode dir_index filetype sparse_super large_file uninit_bg > Journal inode:            8 > Journal backup:           inode blocks Convert ext3 to ext4 Convert an ext3 to ext4 filesystem, use the command. # tune2fs -O extents,uninit_bg,dir_index /dev/mapper/vg0-lvol0 tune2fs 1.41.12 (17-May-2010) Please run e2fsck on the filesystem. After running this command we MUST run fsck to fix up some on-disk structures that tune2fs has modified. # e2fsck /dev/mapper/vg0-lvol0 e2fsck 1.41.12 (17-May-2010) One or more block group descriptor checksums are invalid.  Fix<y>? yes Group descriptor 0 checksum is invalid.  FIXED. ... Group descriptor 79 checksum is invalid.  FIXED. testfs contains a file system with errors, check forced. Pass 1: Checking inodes, blocks, and sizes Pass 2: Checking directory structure Pass 3: Checking directory connectivity Pass 4: Checking reference counts Pass 5: Checking group summary information testfs: 11/655360 files (0.0% non-contiguous), 79696/2621440 blocks WARNING: You cannot revert or mount back to ext3 filesystem once you run above command.