By default, an ext3 filesystem will reserve 5% of its capacity for special processes that can continue to run when diskspace is running low. Here’s the explanation according to the manual.
Specify the percentage of the filesystem blocks reserved for the super-user. This avoids fragmentation, and allows root-owned daemons, such as syslogd(8), to continue to function correctly after non-privi-leged processes are prevented from writing to the filesystem. The default percentage is 5%.
On large partitions (say 8TB+), losing 5% of these reserved blocks for only those processes is quite a lot.
Check your current reserved blocks on your disk
First, check which mount you want to investigate.
$ df -h Filesystem Size Used Avail Use% Mounted on /dev/partition 198G 180G 14G 93% / /dev/sda1 99M 41M 54M 44% /boot tmpfs 2.0G 0 2.0G 0% /dev/shm
In this case, I want the root partition (/), so I’ll do the rest of the examples with /dev/partition.
You can check your current reserved blocks value with tune2fs.
$ tune2fs -l /dev/partition | grep 'Reserved' Reserved block count: 120542571
In this case, it means we’ve ‘lost’ the ability to use 120.542.571 blocks on the partition.
Lower Reserved Blocks by percentage
You can lower the 5% barrier if you like, but I only suggest doing this for larger partitions. Since the default is 5%, I’ll lower it to 2% here.
$ tune2fs -m2 /dev/partition tune2fs 1.39 (29-May-2006) Setting reserved blocks percentage to 2% (48223887 blocks)
With the ‘-m’ parameter you can specify a percentage amount of reserved blocks to keep for that purpose.
-m reserved-blocks-percentage
Set the percentage of reserved filesystem blocks.
After the command, the Reserved Blocks will be lower.
Lower Reserved Blocks by an absolute value
If you prefer to use a fixed set of blocks, instead of a percentage, use the -r parameter.
$ tune2fs -r 48223887 /dev/partition tune2fs 1.39 (29-May-2006) Setting reserved blocks percentage to 2% (48223887 blocks)
With the -r option you get more control, the -m allows you to change things quickly.