> Expanding storage with Linux device mapper involves failing and replacing each storage device
The same process is generally true of mainstream enterprise controllers such as Dell PowerEdge/PERC and HPe ProLiant/SmartArray; each existing drive is failed out (in turn) and the RAID rebuilt onto the new larger drive, then the controller array container is expanded once all drives are replaced.
> It supports surprisingly smart heterogenous drive size utilization while still maintaining N-Drive redundancy: with, for example, a 2TB+4TB+6TB+8TB drive combination
You can do this yourself with ease by creating 2TB partitions on all drives and setting up RAID separately on each. Then you could use LVM to access them as unified storage, or keep them separate for extra flexibility when restoring.
It's theoretically possible but I'm afraid of operation failure for such complex array. So It's nice to have simple user interface like Synology.
You can also replicate Dropbox quite trivially by getting an FTP account, mounting it locally with curlftpfs, then use SVN or CVS on the mounted filesystem [1]
What parameters are you using to make btrfs waste 6TB? With 2 copies (RAID1) and 2+4+6+8, that calculator shows it with 0 unusable space?
Re:Don’t Be Afraid of RAID
by matheusmoreira on Sunday May 24, 2020 @05:41PM
(#23295076)
I used RAID 6. That's 1 copy and 2 parity stripes.
Ah that explains it. Don't use parity with btrfs (i.e. RAID5/6). If you really want that, that's a good reason not to use btrfs.
Re:Don’t Be Afraid of RAID
by matheusmoreira on Sunday May 24, 2020 @06:27PM
(#23295442)
Because of the write hole, right? I've been avoiding btrfs because of that issue. Multiple copies are too wasteful and the parity implementation isn't perfect. Hope it gets fixed soon.
This is their best feature in my opinion. It allows users to just buy random drives from time to time and add them to the NAS when they need to expand storage capacity. Unraid also offers a similar feature albeit with a different implementation.
Current open source solutions just don't compare. Expanding storage with Linux device mapper involves failing and replacing each storage device:
https://raid.wiki.kernel.org/index.php/Growing
Even btrfs wastes 6 TB when given its 2+4+6+8 TB example:
https://carfax.org.uk/btrfs-usage/index.html
I wonder why existing systems can't support this easy expansion. It'd be a huge help for home users who'd like to slowly expand their storage capacity.