Available Storage and Actual Usage

[MrBean]

I have a couple questions in regards to the size of my raidz2 pool. It consists of 10x6tb WD Reds. This is for a new NAS build.

Question 1.
Given that a 6Tb drive has only 5.45Tb of usable space, you can assume the following.
10 drives gives you 54.5 total.
Raidz2 will leave you with 43.6Tb usable.

When I created the pool in FreeNas it showed 54.5 available for the vdev. This is spot on. For the initial dataset it only showed 40.2Tb. Where has the missing 3.4Tb gone? This is too high to be a reservation for metadata.

Question2.
Any file which I copy or create on the pool appears to have a minimum "Size On Disk" of 1Mb. One directory containing 1600 files is only 28.4Mb but using 1.56Gb. Is this correct?

I need to try and sort these questions quickly before I transfer my data. Any help is appreciated.

 

[cyberjock]

Well, that zpool was clearly not made by FreeNAS, so I am definitely not going to put forth more effort on this subject. When one decides to not follow the manual for proper usage of FreeNAS, the behavior and performance will definitely vary from what is expected.

As I (and probably nobody else on this forum) are trying to use FreeNAS in the way you are), you are likely to see no further responses as you are trailblazing your own path on how FreeNAS works for you. So I do wish you luck.

 

[MrBean]

Hi cyberjock.

I am not trying to do anything unsupported as I know this can lead to issues further down the line. I am just troubleshooting to figure this out before I settle down and create the final pools. I did follow the guidelines but had the same issues.

My process so far:

1. Create the pool through the web gui. 2gb partition and zfs partitions where created
2. Observed the incorrect available space and "Size on Disk"
3. Destroyed the pool
4. Created the pool through the shell.
5. Exported the pool
6. Imported the volume through the web gui.
7. Observed the same incorrect available space and "Size on Disk"

This tells me that the issue might not be related to FreeNAS but with ZFS itself or with my drives somehow. I've been searching for answers all day but haven't come up with anything.

Here is the pool, recreated through the GUI showing the same data. There is still 3.4Tb missing and the minimum file size is still 1Mb.

 

[Ericloewe]

Roughly 5% capacity is hidden away to remove incentives to fill 'er up as high as she goes. It's reserved to allow file deletions, IIRC.

 

[MrBean]

Thanks fro the reply. I noticed in cyberjock's signature that he has the same drives and the same number. He is also getting the equivalent usable space so I'm ok with that.

Any idea on why windows reports 1Mb as the minimum "Size on disk"? I have created a large number of 1kb files which all show this. Windows reports the "Size" as a few hundred Kb but the "Size on disk" as over 1Gb. The ZFS usage through the shell appears to report correctly tho.

Is this something I should be worried about? Is my space going to be eaten up by nothing or is ZFS/CIFS reporting this incorrectly to Windows?

 

[SweetAndLow]

I bet windows is failing to report it correctly. I remember reading this at some point.

 

[Hubris Won't Be Tolerated]

Is there a formula that be used to approximate how much space will useable in a dataset approximate to it's zpool(s) size(s)?

It seems the end size values vary widely, as the gentleman above with a 54.5TB zpool and 40.2TB dataset is ~26.5% of the zpool size.

I have a smaller configuration in raidz1 (17TB/5TB,5TB,4TB,3TB; ~15.5TB usable) and my zpool size is 9TB with a dataset usable space of 6.3TB, or 30% of zpool size.

Am I getting a lower percentage of usable space due to not having the "ideal" raidz config (i.e. all disks of the same size)?