BTRFS Volume Smaller Than Raid Calulator

[cwalkin]

Hey All,

Quick question, I have 4x 4TB Ironwolfs in a ds920+, I noticed that the total SHR size is only 10.5TB.
Synology calculator shows it as 12TB. Is this normal?
Im pretty sure I built the pool with all 4 4TB drives in it.

I am also setting up a ds918+ that had 1x 2TB and 2x 1TB and am adding 4 Tb drives and the size of pool also seems to small.

Any help appreciated
Dan

 

[Rusty]

Is this normal?

Yes, note No8 on the calc root page:

Results from RAID Calculator should be used as a reference only (here we use the decimal prefix for the calculation of disk-array capacity. However, since Synology DSM is using binary prefix as calculation base, the conversion error might exist without further clarification.) and should be checked with a certified Synology sales or support representative. Synology makes no guarantees for results generated with this tool.

 

[Rusty]

I am also setting up a ds918+ that had 1x 2TB and 2x 1TB and am adding 4 Tb drives and the size of pool also seems to small.

Adding a new disk to an existing pool is not something that you can calculate using the raid calculator. Calculator is only valid for the new, unused array.

 

[Telos]

I have 4x 4TB Ironwolfs in a ds920+, I noticed that the total SHR size is only 10.5TB

This is correct. Google "TB vs TiB"

 

[jeyare]

Quick question, I have 4x 4TB Ironwolfs in a ds920+, I noticed that the total SHR size is only 10.5TB.
Synology calculator shows it as 12TB. Is this normal?

4TB in decimal is 3.63TiB in binary
then
SHR based on 4x4TB = 3x 3.63TiB (one for parity) = 10.9TiB in RAW

vs Syno RAID calc:
4x4TB in SHR = 3x4TB = 12TB = 10.9TiB in RAW

same numbers

 

[Telos]

And while we're "reducing" your available storage, your volume will be reduced a bit due to take up by the OS and swap partitions. Additionally ... there is a "btrfs tax" amounting to approximately 4% (ext4 is "tax-free"... until you invoke Synology Drive versioning... at which time the "btrfs tax" will look attractive).

It's kinda like my phone which "promised" huge storage... but not all that "storage" was mine

 

[cwalkin]

Hey, Thanks for all the replies. This makes sense now.

Dan