Is it true that a RAID 1 can only be as big as the smallest disk? If it is true, then ten 1GB disks in RAID 1 should only amount for only 1GB of total available space.

Is it true that RAID 1 capacity is limited to 50% of the available drives? If it is true, then ten 1GB disks in RAID 1 should amount for 5GB of total available space.

In some sites I read RAID 1 capacity is 50%, in other sites I read RAID 1 capacity won't ever be larger than the smallest of the disks.

So if you got asked, what's the capacity of ten 1gb disks in RAID1, what would you answer and why? I need clarification.



It all depends on how you set it up.

With ten disks in RAID 1, you get a single disk capacity, with plenty of redundancy: if any 9 disks fail, the data is still there on the single remaining disk. This sounds weird but sometimes you see it as a mdadm RAID 1 for the /boot partition, while everything else is RAID 5/6/10 - which the bootloader might not know how to handle.

You could also do five separate RAID 1, with 1GB capacity each and a single level of redundancy. But if that's your goal, you'd probably just go with RAID 10 instead.

If you have disks of different sizes, you can partition them and then choose an appropriate RAID level for each set of partitions (akin to Synology Hybrid RAID).

If you don't do that, yes it's possible to have (a lot of) wasted capacity in a RAID set. With the exception of mdadm raid0, that additional capacity simply is unavailable until you replace the smaller disks with larger ones. That's why it's common to use same-sized disks for RAID.

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