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TB Hard drives in Synology Disk Station DS409

Medium Priority
Last Modified: 2013-11-14
Hello experts,

I have purchased a synology ds409 from newegg.com and four 1.5 TB hard drives.

The hard drives show up as 1.36TB, and when i formatted them into a single RAID5 volume, i only have 4TB total on the volume.

Where did the other 2TB of space go? i know some went to the raid config, but why does only 1.36 show up? That's like 140 x 4 = 560GB's.. thats a ton of drive space that is missing.
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That's about right then. Essentially with RAID 5 you get the combined total drive capacity -1 disk so...

4 x 1.5TB = 6TB - 1.5TB = 4.5TB. This is the RAW capacity so the ~4TB formatted capacity you are seeing is correct.


So RAID 5 uses 1 disk for the striping and parity, but the space for this is distributed over an entire disk?

why is the raw capacity for a 1.5 tb drive only 1.36? That's 140GB which is a lot of space and more than my internal hdd on my computer..
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Anything else we can help you with regarding this?


guess not.. didn't know if you were still trying to locate the link. No worries. Thanks a bunch for your help.

Another reason for the loss of space is that the Synology NAS needs to install it's 'OS' onto the drives in order for it to function. This creates a series of partitions which swallows up a reasonable amount of space. It's usually around the 2GB per disk level, so you would be looking at losing another 10GB or so there.
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