Repurpose Drobo 5D3 with BTRFS RAID5

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Repurpose Drobo 5D3 with BTRFS RAID5

DS1621xs+, RS2418+
Operating system
  1. macOS
Mobile operating system
  1. iOS
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Does anyone have experience repurposing a Drobo (5D3) with BTRFS RAID5?

I have an old Drobo setup that has 5 2TB drives I'd like to set up so I can send snapshots to as an additional layer for my backups. Traditionally, this Drobo is a DAS and can be formatted with either NTFS via the Drobo Dashboard tool in Windows or HFS+ via the Drobo Dashboard macOS app. When plugged into my DS1621xs+ there are not any options to format BTRFS despite it being the file system I'm using for the Synology.

I've read mixed reviews from people who have formatted their Drobos with ext3 and ext4 to use with Linux. It's pretty clear that this isn't officially supported by Drobo but curious if anyone has created external RAID arrays for use with BTRFS and ultimately connected to a Synology NAS. If this is possible, I'm hoping to understand the best way to go about setting this up; configure this from a Linux box or by SSH while directly connected to my Synology NAS.
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If the Drobo is DAS then I assum it behaves like and is seen as an external storage device, similar to any other USB (or whatever connection it has) external storage device. Internally I guess it has the ability to manage how its drives are configured, formatted, and how the storage is presented to the host device (the one it is connected to).

If I'm right then the Drobo's storage will have to be formatted into volumes using a file system type that is supported by your NAS. Which for your DS1621xs+ are these types. First time I've notice Btrfs as one of the type for external devices.*

External Drives
  • Btrfs
  • EXT4
  • EXT3
  • FAT
  • NTFS
  • HFS+
  • exFAT

The NAS won't configure RAID on the Drobo, as it only will do this for itself and attached Synology expansion units (e.g. DX517). But the NAS can format volumes/partitions on external storage devices, though I've only seen Control Panel / External Devices options for ext4, FAT32, and exFAT. Other supported file system types have to be prepared elsewhere.

*I just looked at Synology's spec page for my DS1520+ and see Btrfs has been added to it too. And my DS218+ too. Well you live and learn. Still none the wiser how to use it for external devices. I wonder if creating a Basic volume on one drive using Btrfs and then transferring it to a USB enclosure would work... I don't hold out much hope.
The problem you'll hit is that Drobos do thin provisioning & rearrange data across multiple volumes according to their understanding of what blocks are occupied & which are not.
This basically *requires* the Drobo firmware (Linux based) understands the filesystem used & knows which blocks are or aren't in use.

If you reformat the volume a Drobo creates to btrfs you're in for a world of hurt.

All is not completely lost if you really must use btrfs, but your options are limited, and you're restricted to a volume of a fixed size which you have the storage to fully provision.

Your safest option is to create a file based container, a "virtual drive" if you will on the storage with the Drobo itself formatted in a supported file system, & then use Linux to mount the file & format it. Truecrypt/VeraCrypt file based containers are known to work, & you can format a VeraCrypt container to btrfs.

You MIGHT get away instead with creating / enabling the "backup volume" & formatting that to btrfs, again you'll need to have the storage to fully provision it, & you may need to encrypt it to convince the Drobo it's occupied.

Drobo don't talk about it much, but they used to have official beta support for ext3, & some users report ext4 working (since the os in firmware actually uses it & consequently understands it), others hit issues, so your mileage might vary.

I've been seriously considering pointing VeraCrypt at my 5C's backup volume & reformatting to btrfs post-encryption, the backup volume supports encryption at least Apple's encryption for Time Machine, or BitLlocker, given that renders the volume opaque to the device I don't see why VeraCrypt, or dm-crypt/LUKS wouldn't also work, but it's your data, don't risk it unless you're prepared for complete loss & resetting your Drobo & restoring from backup to a file-system they support.
I had pretty much concluded that this probably isn't worth messing with this any further and pretty much abandoned it after a bit of further reading but may attempt going the route of creating a file-based container as you mentioned. I also realize the risk and understand this shouldn't be used as my only backup. I'm simply trying to repurpose a couple of these Drobos that have been sitting around since I don't use them in production anymore and am hoping to add snapshots to a different device than my current Synology box. At this time I will need to acquire another piece of equipment to accomplish this. I guess I can see if there's anyone interested in a couple of Drobo 5D units and just get rid of them.

@Bearded_Blunder thanks for your response, this is very helpful!

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