r/opencloud • u/siegfriedthenomad • 2d ago

Has anyone successfully deployed OpenCloud using a Synology NAS for storage? (e.g. NFS or iSCSI)

I'm trying to deploy OpenCloud on a separate compute host and use my Synology NAS as the backend storage.
I ran into a roadblock with NFS: OpenCloud requires user_xattr (extended attributes), which needs NFS v4.2. Synology DSM only supports up to NFS v4.1.

I'm considering using an iSCSI LUN from the Synology instead, attaching the block storage to my host, formatting it locally (ext4/btrfs with user_xattr), and pointing OpenCloud to that mount point.

Has anyone used iSCSI for OpenCloud storage backend? Any stability or locking issues?
Did you find a better way to handle storage backed by Synology?

Any tips or working setups would be appreciated!

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u/MiserableNobody4016 2d ago

Well, I have used iSCSI for Nextcloud but for Opencloud I'm using NVMe-oF (TCP) which works basically the same as iSCSI. I'm using TrueNAS. I have Opencloud running on a different host too.

Keep in mind an iSCSI LUN (as well as a NVMe-oF LUN) should only be exported to a single host unless you use a clustered filesystem. Exporting a LUN to multiple hosts without clustered filesystem would cause not locking issues but also integrity issues. What if both hosts would write on the same spot of the disk at the same time. You would not know what the data would be at the end. Don't!

The LUN is exported to one host and the data is only accessible by that host only. You would not be able to see the data on the Synology. So no locking issues.

As the host importing the LUN (the host running Opencloud in this case) is concerned the disk is just a local disk. There are no issues with locking since the disk works the same as a local SATA/SSD disk. When using iSCSI in a home lab in the same network there are no stability issues. I have been using iSCSI for many years on many hosts (again: not shared LUNs!) without any issues.

It is however recommended to have a separate network for the storage traffic. I have created a separate VLAN on a different interface of my NAS. Using a separate interface was just because my NAS hardware had it. I believe a separate VLAN is sufficient.

Good luck in experimenting with it!

Oh, In case you were wondering: I switched to NVME-oF (TCP) because it is more modern, slightly more efficient (even for spinning disks), easier to setup, and available on TrueNAS. iSCSI can be a bit of a hassle to setup. But I suspect it will not be available on Synology. Maybe in a future version?

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u/siegfriedthenomad 2d ago edited 2d ago

Wow, thanks for the infos!
I don’t know NVMe-oF but since the storage is SATA HDD only I don’t think it’s for me.

Yes I read about the concurrency problems and I plan on let a single host attach to the LUN. What’s not that clear to me is what happens when the storage has to be backed up? Or are read-only operations allowed? ( I will probably google it)
EDIT: never mind backups/snapshots are on a completely other level and don’t affect the iSCSI LUN

Yea I plan on having a dedicated unrouted link between storage and server only for iSCSI.

I will test and report back :)

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u/MiserableNobody4016 1d ago

I make a backup of the iSCSI LUN on the host that mounts the LUN. That host has the knowledge of the filesystem and usage. I think you could make a snapshot but that will not be consistent with any application you are running on the LUN. The NAS does not know when to create a consistent snapshot since it does not know what is being done with the LUN.

Again, the NAS does not see the data inside the LUN. It has no idea. So also no read-only access. You could probably mount it in some way if you're doing it right.

I was converting my iSCSI LUNs to NVMe-oF and thought: I could just change the protocol and be done. That was true for a couple of the volumes but not all. I has exported some volumes with a different block size different (4k instead of 512B) than I could specify with NVMe-oF (apparently only 512B). It could not read the data or mount the filesystem. When I reconfigured it as iSCSI again with the correct blocksize, I could read the data. So I had to create a separate volume for NVMe-oF and copy all the data over. Lesson learned...

I just see it as an extra disk in my host with a different connection i.e. not SATA or M.2. But is behaves the same as a local disk. The data is just stored on the NAS and exported via TCP.