Storage and Filesystems

These are some tricks and hints to common issues/tasks to deal sometimes

This example is based on resizing the filesystem on the raspberryPi2 SDcard, but should apply to other scenarios

Show partition table, and take note of the output, specially start and end sectors of the partition:

# fdisk -l /dev/mmcblk0
Disk /dev/mmcblk0: 7.4 GiB, 7948206080 bytes, 15523840 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xc96ffe28
Device         Boot  Start     End Sectors  Size Id Type
/dev/mmcblk0p1        2048  249855  247808  121M  e W95 FAT16 (LBA)
/dev/mmcblk0p2      249856 6291455 6041600  2.9G 83 Linux

Note that mmcblk0 is about 7.5Gb, but the filesystem root (partition 2) is only using 3Gb.

Run interactive fdisk over the disk and do the following:

• Delete the parition d
• Create new partition n, same type, number and… exactly the same start sector (249856 in our example)
• Use the remaining space (end sector)
• Write changes to disk w

Now you have to reboot the system, after that, you should be able to see the new partition size:

# fdisk -l
Disk /dev/mmcblk0: 7.4 GiB, 7948206080 bytes, 15523840 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xc96ffe28
Device         Boot  Start      End  Sectors  Size Id Type
/dev/mmcblk0p1        2048   249855   247808  121M  e W95 FAT16 (LBA)
/dev/mmcblk0p2      249856 15523839 15273984  7.3G 83 Linux

Note that now the end sector of the partition is now 15523839, although filesystem is still the same size:

~# df -Th /
Filesystem     Type      Size  Used Avail Use% Mounted on
/dev/root      ext4      2.8G  771M  1.9G  29% /

# resize2fs /dev/mmcblk0p2
resize2fs 1.42.12 (29-Aug-2014)
Filesystem at /dev/mmcblk0p2 is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 1
The filesystem on /dev/mmcblk0p2 is now 1909248 (4k) blocks long.

# df -Th /
Filesystem     Type      Size  Used Avail Use% Mounted on
/dev/root      ext4      7.2G  774M  6.1G  12% /

Although there are tools to resize any extN filesystems, many times don't work out-of-the-box due the default filesystem settings and features used for Linux distros.

Here explain steps and commands to allow that resizing feature. Please keep in mind the usual warn about 'responsability exemption'. Also take note that the process is long (depending on filesystem size and block device).

Is generally recommended to run a e2fsck after any filesystem change (either in size or in metadata/features).

The unique features supported by parted to do a resizing are:

• hasjournal * dirindex
• filetype
• sparsesuper * largefile

Will use some advanced commands like tune2fs and debugfs. With tune2fs you can see the fatures used by the filesystem:

tune2fs -l /dev/sda1 | grep features

The following command shoulds remove these faetures:

tune2fs -O ^ext_attr,^resize_inode /dev/sde1
debugfs -w -R "feature -ext_attr -resize_inode -dir_index"

Now, check/fix filesystem

e2fsck -f -y -v $DEV

Do the resize

Check/fix filesystem again

e2fsck -f -y -v $DEV

Restore the features removed before:

debugfs -w -R "feature ext_attr resize_inode dir_index" $DEV

Check/fix filesystem again

e2fsck -f -y -v $DEV

rsync is the best tool to guarantee identic replication (including hardlinks) but may require a huge amount of memory and will be slow on the first initial sync.

Best is to use cpio and just after, sync again:

find . -xdev -depth -print | cpio -pdum $DESTINATION
rsync -au -x -H --devices --specials --size-only --stats $SOURCE $DESTINATION

I deveveloped a handy script dataMover.sh for that

If you are moving the rootfs from one device to another (for example a new disk), you will need to setup grub loader.

Supposing you already copied all the rootfs filesystem to the new partition, to setup the boot chain follow as:

mkdir -p $TEMPROOT
parted $DISK set $PART boot on
mount $NEWDEV $TEMPROOT

Mount the some virtual filesystems needed on it:

mount -o bind /dev $TEMPROOT/dev/
mount -t proc none  $TEMPROOT/proc/
mount -t sysfs none $TEMPROOT/sys/

Now will run grub inside a chroot environment inside the new ddisk:

chroot $TEMPROOT /usr/sbin/update-grub
chroot $TEMPROOT /usr/sbin/grub-install $DISK

To finish umount everything so all data is flushed to disk.