Create volume - 8% space used right away ?

[Child]

Hi guys,

I'm just setting up a freeNAS machine. Now I think there's an issue which I'm not able to resolve by myself.

I want to create a volume of a 500 GB (~488 GiB) HD. File format should be UFS. It works fine and all. But the size of the volume is just way of as you can see in the picture.



But it's not so much the total size I'm wondering about. It's more the amount available and that there's already 8% used from the start.

Anyone any suggestions?

 

[Brand]

I don't see what the problem is, that is how it is designed.

 

[Child]

Thx for your answer Brand.
As stated in my post I was just wondering because it just seems a bit odd. Is there any reason why it is designed that way? If you imagine someone setting up like 12 TB HD space and losing 8% right from the beginning. That's a large junk of storage space.

 

[Milhouse]

By default UFS will reserve 8% on the disk for root - apparently it's so that defective sectors can be reallocated automatically.

You can change the reserved percentage at the command line using tune2fs, something like:

Code:

tune2fs -m 6 /dev/sda1

would change the reserved percentage to 6% - it won't affect any data already on the disk.

It's not recommended to set the reserved percentage to 0%, but a percentage as low as 3% should still be OK.

 

[ACGS]

Thxs, Milhouse. I have a 5.37 TB RAID arrray on an NAS holding 1.7 TB data. Windows shows space used as 2.1 TB. I wanted to reduce that difference and your post gave me the solution.

Would 2% be a safe setting. If not, I will use 3% per your previous 9-28-2011 post.

 

[Milhouse]

I personally wouldn't go below 3%, but 2% should still be OK.

 

[Child]

hm ... I did a check:

Code:

~# egrep 'ada[0-9]|cd[0-9]' /var/run/dmesg.boot
ada0 at ahcich0 bus 0 scbus0 target 0 lun 0
ada0: <ST2000DL003-9VT166 CC32> ATA-8da0 at umass-sim0 bus 0 scbus6 target 0 lun     0
ada0: 300.000MB/s transfers (SATA 2.x, UDMA6, PIO 8192bytes)
ada0: Command Queueing enabled
ada0: 1907729MB (3907029168 512 byte sectors: 16H 63S/T 16383C)

and then tried this command:

Code:

~# tune2fs -m 4 /dev/ada0

but I only get an error:

Code:

tune2fs 1.41.14 (22-Dec-2010)
tune2fs: Operation not permitted while trying to open /dev/ada0
Couldn't find valid filesystem superblock.

 

[delphij]

For data disks it should be Okay to just set reserved space to 0%.

The point of having reserved space is primarily based on two considerations: a) any rotating disk file system, including UFS, needs to avoid so-called "file fragmentation" (not the UFS "fragment", which is the smallest allocation unit in UFS and thus different concept), and no algorithm can work well when the available space drops to a certain level. Having reserved space makes users aware of the problem before the situation became very bad; and b) if system log is written to that file system, the "root" user still can write while non-privileged users are blocked from writing new data, allowing the system to write down critical log data in emergency case.

 

[delphij]

tune2fs is for ext2fs, are you sure it's the case?

I think the following might work for you in your case (note that you need to operate on the special file containing the file system, which is not likely be a whole device):

tunefs -m 0 /dev/ada0p2

Note that the above example tunes reserved space to 0%.