newly added 4TB drive shows 4GB used, but it's empty

[JustinChase]

I'm not terribly concerned about 4GB, but I don't know where it's been used.  I've checked by hitting the folder icon on the array devices tab, and also via putty and midnight commander.  both show the drive as having no files, but the array devices tab shows 4.02GB being used on this drive.

 

what's up?

[JorgeB]

It's normal for the xfs filesytem, about 1GB per TB.

[tdallen]

edit, cross posted with Johnnie who answered the question.

Edited January 19, 2018 by tdallen

[JustinChase]

4 minutes ago, johnnie.black said:

It's normal for the xfs filesytem, about 1GB per TB.

 

hmmm...  I didn't think that was the issue, based on a 2TB drive I just emptied, which shows it only using 34MB

[JorgeB]

If you reformat it you'll get ~2GB used

[JustinChase]

weird.  I wonder why it takes 2GB if I format (erase everything), but 34MB is I just empty it.  What's taking up the 2GB?

[JorgeB]

Don't know, ask an xfs maintainer, it's likely some metadata reserve for filesystem housekeeping, can only tell that it's normal.

 

 

[JorgeB]

Also let me add that the 2TB was probably formated with an earlier xfs version, and that's the likely reason it was emptier, xfs started using more space on newer kernels, IIRC a couple of years ago or so.

[JustinChase]

Also let me add that the 2TB was probably formated with an earlier xfs version, and that's the likely reason it was emptier, xfs started using more space on newer kernels, IIRC a couple of years ago or so.

that would make sense, it was formatted years ago, just after xfs was added to unraid

Sent from my HTC6545LVW using Tapatalk

[pwm]

14 hours ago, JustinChase said:

weird.  I wonder why it takes 2GB if I format (erase everything), but 34MB is I just empty it.  What's taking up the 2GB?

Your drive is most probably formatted with an older version of XFS.

 

It's common that newer versions of FS adds support for new features and so also increases the size of internal data structures. If an FS adds support for checksums on all meta-data, then the newer data structures must has room for storing the checksums. But in general, there are lots of optimizations happening in newer FS versions. Some also needed to make the FS work better with larger disks.

[JustinChase]

2 hours ago, pwm said:

Your drive is most probably formatted with an older version of XFS.

 

It's common that newer versions of FS adds support for new features and so also increases the size of internal data structures. If an FS adds support for checksums on all meta-data, then the newer data structures must has room for storing the checksums. But in general, there are lots of optimizations happening in newer FS versions. Some also needed to make the FS work better with larger disks.

 

hmmm...

 

seems like re-formatting it might be a good thing.  How do i do that while it's in the array?  it's empty now.

[JorgeB]

8 minutes ago, JustinChase said:

How do i do that while it's in the array? 

Change filesystem to reiser or btrfs, start the array, format, change back to xfs and format again.

[SSD]

@JustinChase -

 

Chasing 2G on a disk that is 4T is not so productive. That is 1/2000th of the disk. 0.05%. 

 

The disk requires some amount of space for the housekeeping areas. Improvements to the filesystem (to allow better recoverability or performance, for example) might up the size of this area slightly but are worthwhile.

 

Use the disk and enjoy!  

[JustinChase]

I think you misunderstood.  I was originally only asking why the difference in 2 empty disks.  After learning about the increased functionality, I asked how to reformat the old 2TB drive to gain the advantages of the new file system improvements, and am willing to give up the 2GB to get said advantages.

[JustinChase]

On 1/20/2018 at 11:46 AM, johnnie.black said:

Change filesystem to reiser or btrfs, start the array, format, change back to xfs and format again.

 

That worked great.  My 2TB drive now uses 2GB after reformatting.  i hope I never need the improved recovery stuff, but good to know it's there.

 

not sure it's worth moving all my files off of the other drives to reformat them, but I did consider it.

[JonathanM]

7 hours ago, JustinChase said:

not sure it's worth moving all my files off of the other drives to reformat them

If the drives were filled in an orderly fashion, probably not worth it. On the other hand, if you are in the habit of deleting stuff, moving files from one drive to another to "balance" things, overwriting files, all the activities that produce some measure of fragmentation, then perhaps it might be worth it just to get a clean fill. Drives that are thrashed are a little harder to recover, as they are less predictable as far as physical file location when the recovery software is used.

 

Since modern file systems are designed so fragmentation is not a huge issue any more, defragmenting a drive isn't really a thing. Formatting and putting the data back in one contiguous copy operation will defragment it.

[Unraiding]

Just adding my thanks and experience.  New 12TB drives formatted as XFS ended up with ~84GB used.

 

[bombz]

Here he a comparison for anyone interested for the visual difference.
Cheers

Edited March 9, 2021 by bombz

[JorgeB]

5 hours ago, bombz said:

Perhaps I will attempt the format (change file system and back to XFS) once parity sync has completed to see if the used space differs

It won't. 

[bombz]

2 hours ago, JorgeB said:

It won't. 

Indeed. Was more curious then anything.
Thank you kindly :-)