Available Space Question

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HDNewbie1028

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I am setting up my first home server, and am a complete n00b so forgive me if I don't provide all the information at first since I don't know what all you would need. Perhaps this is a simple question, but I could not find the info on this forum.

I turned on my FreeNas for the first time last night. I am running the latest version on an ASUS Micro-ITX Motherboard with 16GB of Crucial Ballistic Non-ECC RAM. The FreeNas is running on an 8GB USB stick plugged into a USB 3.0 port on the back of my case.

I have set up 4 - 4 TiB HDD in a RAID Z2 (16 TiB total) for my NAS. I used the Volume Manager option to create my RAID Z2.

I did not change any settings when creating the volume. My assumption was that I would end up with 8 TiB of available storage with the other 8 TiB as the redundancy. It is telling me what I actually have is 6.9 TiB of available space. Compression is set to lz4 and the compression ratio is 1.00x The status of the 4 drives are healthy.

My question is, why did I lose an additional 1.1 TiB of storage? Did I do something incorrectly when i set up the volume? Do I need to get rid of the volume and start over again? Or is that much available space normally lost when creating a volume with a 4 TiB HDD RAID Z2?

I did play around with adding datasets, just to familiarize myself with the process, but the available storage issue was present before I started adding datasets.

The funny thing is, when I first used the volume manager to create the volume it had estimated the capacity to be 7.2 TiB. The Volume Manager did hang on me so after five minutes I closed that window and reopened it. The volume had been created, but the available storage had dropped from 7.2 TiB to 6.9 TiB.

I looked at a RAID converter on another site, and they indicated only 1.56% of storage would be used by ZFS for metadata, which, if that is true, would still give me just under 8 TiB for storage.

So, is this normal and expected, or did something happen that shouldn't? I don't wish to start moving any files over to the FreeNas until I know it is set up with the most available storage and the redundancy ratio is correct.
 

HDNewbie1028

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Reading a couple posts down I see someone else with a similar issue and block size is mentioned. Could this be the answer to my post?
 

david kennedy

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Dec 19, 2013
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I have set up 4 - 4 TiB HDD in a RAID Z2 (16 TiB total) for my NAS. I used the Volume Manager option to create my RAID Z2.

My assumption was that I would end up with 8 TiB of available storage with the other 8 TiB as the redundancy. It is telling me what I actually have is 6.9 TiB of available space. Compression is set to lz4 and the compression ratio is 1.00x The status of the 4 drives are healthy.

Using a raid calculator on the net shows you have:
*Raw Storage: 16.0 TB / 16000.0 GB
*Usable Storage: 7.3 TB / 7450.6 GB

So after some small accounting issues you are close to the theoretical values (6.9 vs 7.3).
This is probably due to the old 1000 vs 1024 issue with drives.

You said you played around a bit. Any chance you copied data over and created a snapshot of it?
 
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