Storage Explanation Needed

[AstroCEO]

Can someone explain to me why these four 18TB HDDs show up as these three different file sizes shown below?



I know that the real size of the 18TB comes out to the 16.4TB, but wouldn't that mean I have the full 32.8TB for my Raid 10 Volume?

Why do I only have 31.4TB according to the Storage Manager, and the settings strangely says 33.5TB in modify size?

 

[fredbert]

Storage is 2x 16.4 TB = 32.8 TB (or 32.7 as shown, for rounding). It doesn't say 33.5 TB it says 33,507 GB: divided by 1,024 gives you the 32.7 TB.

You have probably used Btrfs file system and that uses an amount of the storage for maintenance and protections. This is likely the reason you see the volume is 31.4 TB.

 

[AstroCEO]

Gotcha, I did use BTRFS, because it sounded like it had a lot of advantages after looking into it more, and it's more native to Synology. If I used FAT32 or NTFS, or whatever alternatives are available, it would likely have been precisely 32.7TB for Volume 1 like shown?

 

[fredbert]

The only alternative is Ext4. Some packages need Btrfs in order to work. You also can use snapshots/replication. So it really depends what NAS you have (you can add this to your profile) and what you aim to use the NAS for.

Which file system should I use to create a volume? - Synology Knowledge Center

Synology Knowledge Center offers comprehensive support, providing answers to frequently asked questions, troubleshooting steps, software tutorials, and all the technical documentation you may need.

kb.synology.com

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Checked my Array vs Volume (Btrfs) sizing and it's 21.8 TB vs 20.9 TB. And this ratio is the same as you have. That's ~4.13% 'lost'.

 

[EAZ1964]

Any specific reason (like 10GBE) to use a RAID10?
The speed advantage is low, and the redundancy is 50% so low efficiency on disk space.

 

[AstroCEO]

@fredbert, that checks out. Thank you so much!
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I'm using RAID 10 with 4 drives for 4x Read/2x Write, with quick rebuild times, and less cost for replacement or upgrade. Six drives is 6x the cost of an upgrade, and 2 more drives that can fail. Rebuild times are much quicker than parity with a full copy to draw data from. The only real drawback is the drive space halving, but that's worth the benefits in my opinion.
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@EAZ1964