Newly formatted disk has 7.5Gb used space.

[adgilcan]

Hi

 

I have just added a 1050Gb SSD disk to my array and formatted it to XFS.  I notice that it starts its life on the array empty but with 7.5Gb space already used.  This seems like an awful lot to me.

 

Is this normal?

 

Thanks

 

D

[ConnerVT]

Yes.  File system overhead.  7.5GB is 0.7% of the 1TB drive.

[neohidra]

Indeed - it is because by default Unraid formats disk with Reflink enabled.

I see no point in using this feature since it will consume around 0.7% of the available disk space.

 

You can find example of how to manually format disk, but I do something like this.

In case the drive is already part of the array you have to:

1. stop the Array (Main > Array Operations > Stop)
2. change the disk File system type to something else (Main > Array Devices > Disk # > File system type:)
3. start the Array (Main > Array Operations > Start)
4. now format the drive manually
5. stop the Array
6. change back the File system type of the disk to XFS
7. start the Array

 

Unraid 6.11 by default is producing XFS drives with the following properties:

Apr 8 00:37:06 Tower emhttpd: shcmd (270): xfs_growfs /mnt/disk2

Apr 8 00:37:06 Tower root: meta-data=/dev/md2 isize=512 agcount=6, agsize=268435455 blks

Apr 8 00:37:06 Tower root: = sectsz=4096 attr=2, projid32bit=1

Apr 8 00:37:06 Tower root: = crc=1 finobt=1, sparse=1, rmapbt=0

Apr 8 00:37:06 Tower root: = reflink=1 bigtime=1 inobtcount=1

Apr 8 00:37:06 Tower root: data = bsize=4096 blocks=1465130633, imaxpct=5

Apr 8 00:37:06 Tower root: = sunit=0 swidth=0 blks

Apr 8 00:37:06 Tower root: naming =version 2 bsize=4096 ascii-ci=0, ftype=1 Apr 8 00:37:06 Tower root: log =internal log bsize=4096 blocks=521728, version=2

Apr 8 00:37:06 Tower root: = sectsz=4096 sunit=1 blks, lazy-count=1

Apr 8 00:37:06 Tower root: realtime =none extsz=4096 blocks=0, rtextents=0

 

In order to disable reflink option  you have to reformat the disk - which means that the data stored on this device will be lost.

With the command bellow you can format (data will be erased from the device) disk /dev/md2:

mkfs.xfs -m crc=1,finobt=1,reflink=0 -l su=4096 -s size=4096 -f /dev/md2

 

This way on 6TB you should get about 40GB additional space compared to the default formatting in Unraid.

Edited May 23, 2023 by neohidra
More accurate values

[adgilcan]

Thank you very much.

[adgilcan]

1 hour ago, neohidra said:

Indeed - it is because by default Unraid formats disk with Reflink enabled.

I see no point in using this feature since it will consume around 0.7% of the available disk space.

 

Thank you

 

This feature seems to be of help with speeding up copying and duplication of data.  I have no idea how useful this would be to me in the real world but I wonder why UnRaid would incorporate it if it wasn't of much use.  Would anyone from the moderation or Limetech staff like to jump in here?

Nevertheless, I appreciate your thoughts, @neohidra  It's always good to learn new things!

 

D