Missing Disk space

[psusi]

You may not want to remove the 5% reservation. Any time you fill the disk above 90% it is going to start getting heavily fragmented, so it's a good idea to NOT fill it up all the way.

[mikechant]

You may not want to remove the 5% reservation. Any time you fill the disk above 90% it is going to start getting heavily fragmented, so it's a good idea to NOT fill it up all the way.

If you are filling up a large partition with lots of media files over time, but not editing these files subsequently, they will not be very fragmented and keeping the reserved area reserved will just be a waste.
And fragmentation only really matters when it gets bad enough to cause some sort of stuttering or dropouts when playing media files, which is unlikely on modern hardware.

[brallan]

So, if I format it ext4, then it by default 5 percent of the partition space is reserved for root use? Sounds like it might have been what was going on. I had never before used ext4 for a usb drive, and was unaware of that.

how can one see if there is space reserved for root on a partition? And how does one keep that space from getting assigned to root?

Thanks for all of your help. In the end I simply decided to repartition the drive in light of the error gparted gave me, and chose NTFS since it has always worked for me in the past.... I am using two 500GB disks to back up a single terabyte disk, so having that extra 5% is important. 12 hours later, the backup is done.

[mikechant]

If you add together the 'used' and 'avail' amounts from "df -h" then subtract the total from the 'size' amount this will show how much space is reserved, i.e. using the "df -h" output from your original post in this thread:

reserved = free - (used + avail)
= 459G - (435G + 807M)
= 459G - 436G approx
= 23G

Note that 23G/459G = 0.05 = 5% reserved

My earlier post in this thread:
http://ubuntuforums.org/showpost.php...53&postcount=7
shows the tune2fs command to reduce or remove the reserved space.


One further thought is that maybe on a backup drive it could be worth leaving 1-2% reserved as a warning - i.e., you hit 'disc full', remove the reserved space and successfully complete the backup, but you've been warned that you're nearly out of space and have a bit of time to take some action before your disc is really completely full.

[psusi]

If you are filling up a large partition with lots of media files over time, but not editing these files subsequently, they will not be very fragmented and keeping the reserved area reserved will just be a waste.
And fragmentation only really matters when it gets bad enough to cause some sort of stuttering or dropouts when playing media files, which is unlikely on modern hardware.

Yes, they will be. The less free space is left on the disk, the less large free extents there are, so putting one more large file on to use up the last of the space will leave it VERY fragmented.

[mikechant]

Yes, they will be. The less free space is left on the disk, the less large free extents there are, so putting one more large file on to use up the last of the space will leave it VERY fragmented.

In the extreme case where all files are written sequentially one at a time (like a tape backup) you will get exactly zero fragmentation on any sensible filesystem - every file, including the last one that fills the disc, will get a contiguous space allocation.
What I am asserting is that for drives full of large media files where deletions and updates are very rare, the real life case will be very close to this situation. This is based on at least one assumption - that bittorrent clients generally reflect the behavior of the ones I have used, where they allocate entire files in one chunk, in one operation, at their full size (and fill in the actual data in place later). Also it assumes that a typical disc copy operation using cp, rsync etc. when copying multiple files essentially copies one file at a time rather than interleaving them.
Essentially, I'm saying that certain common patterns of media file accumulation where files are typically allocated in one operation, or one file at a time, and never updated or deleted subsequently, does in fact lead to the filesystems being written to in an entirely sequential pattern with zero fragmentation.
The odd deletion or update will give some fragmentation but it will not be significant because the deleted areas will still be large and will typically only end up in making the odd file use 2 extents rather than one.
Using different tools/applications etc. to obtain media files may in some cases introduce fragmentation but this will typically be localized (e.g in some cases downloading three single music tracks simultaneously will lead to these files being interleaved but the three files as a whole will form one contiguous blocks and subsequent space will still be contiguous).

to remove any doubt, I'm *not* talking about any filesystems which include such things as the browser cache which will typically be being updated frequently in small chunks. This alone will cause serious fragmentation in that filesystem. I'm talking specifically only about filesystems dedicated to large media files.

Apologies if this is a bit rambling/repetitive, I'm "celebrating" the royal wedding in the traditional British way by consuming large amounts of alcohol!