Check the reserved block percentage of an Ext2/3 filesystem

dumpe2fs -h /dev/sdX

You are probably aware that some percent of disk space on an ext2/ext3 file system is reserved for root (typically 5%). As documented elsewhere this can be reduced to 1% with tune2fs -m 1 /dev/sdX (where X = drive/partition, like /dev/sda1) but how do you check to see what the existing reserved block percentage actually is before making the change? You can find that with dumpe2fs -h /dev/sdX You get a raw block count and reserved block count, from which you can calculate the percentage. In the example here you can easily see that it's currently 1%, so you won't get any more available space by setting it to 1% again. FYI If your disks are IDE instead of SCSI, your filesystems will be /dev/hdX instead of /dev/sdX.

Sample Output

...
Block count:              137128831
Reserved block count:     1371288
...

-2

By: dmmst19

2011-01-22 23:50:03

dumpe2fs

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Check the reserved block percentage of an Ext2/3 filesystem

Just change /dev/sda1 to whatever your partition of interest is. This snippet should do the rest. Show Sample Output
This is sample output - yours may be different.
```
Reserved blocks: 5%
```
0

dumpe2fs -h /dev/sda1 2> /dev/null | awk -F ':' '{ if($1 == "Reserved block count") { rescnt=$2 } } { if($1 == "Block count") { blkcnt=$2 } } END { print "Reserved blocks: "(rescnt/blkcnt)*100"%" }'

MichalBryxi · 2011-03-14 20:46:56 4

What Others Think

When an ext-based filesystem has less than 5% free space, there can be significant performance reduction due to fragmentation. So it's generally not advisable to set the reserved block % below 5%, but if you are in a situation where you're willing to take the performance/fragmentation hit, at least you have the option with this command.

dmmst19 · 458 weeks and 1 day ago

avideh · 152 weeks and 2 days ago

rahimhh21 · 124 weeks and 4 days ago

Perfecthomepugs · 115 weeks and 4 days ago

pugpuppies95 · 77 weeks and 5 days ago

yeneba6574 · 32 weeks and 3 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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