Linux Disk Space: ext filesystem reserved blocks

author — Wed, 18 Jan 2023 13:59:46 +0000

With an ext filesystem 5% of disk space is by default reserved for privileged processes/root user.

This allows the system to keep functioning even if non-privileged users fill up all the space available to them.
Important tasks and system processes will still be able to work and write to the drive.

NEVER set it to 0 for a system partition
tune2fs reservation changes happen immediately

# tune2fs -m  /dev/

Set the percentage of the filesystem which may only be allocated by privileged processes.
Reserving some number of filesystem blocks for use by privileged processes is done to avoid filesystem fragmentation, and to allow system daemons (root-owned daemons) , such as syslogd(8), to continue to function correctly after non-privileged processes are prevented from writing to the filesystem.

The default percentage of reserved blocks is 5%

See also: mkfs.ext4 with option -m (reserved-blocks-percentage) to create an ext4 filesystem

For a large ext filesystem used for system partition you may reduce it to 1% of disk space:

# tune2fs -m 1 /dev/

For an ext filesystem that only acts as storage you may disable it:

# tune2fs -m 0 /dev/
# tune2fs -r 0 /dev/

Set the number of reserved filesystem blocks directly:

# tune2fs -r

Example for 3GB of reserved filesystem 4K blocks:
1GB = 1024^3 bytes = 1073741824 bytes

3GB = 3 x 1073741824 = 3221225472 bytes
3GB = 3221225472 bytes / 4096 bytes = 786432 blocks

# tune2fs -r 786432

disk Archives - ITEC4B

Linux Disk Space: ext filesystem reserved blocks