Advice Needed - Proxmox PBS "Special Device"

[void307]

We're building a PBS box for an additional offsite backup with some equipment we have laying around (except drives, they're new)

I've read the majority of the PBS User Manual from page one and it mentions a special device needed for HDD drives.

However, a special device seems risky aka if one or both Nvmes fail, the entire backup pool is lost. (im junior with this kind of thing).

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Referencing "Proxmox Backup Documentation PDF - 19 March 2026"

Section 2.1.2 Page 7 - Backup Storage
Section 13.1.2 Page 117 - ZFS Special Device

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The current bill of materials:

1x Supermicro X10SRL-F

1x Xeon E5 2650v4

128GB ECC DDR4

1x Dual X520 NIC

8x 20 TB WD Gold Enterprise (direct SATA connection to MB)

2x Samsung 900GB or 1.9TB SAS SATA Drives for OS

Special Device (Debatable point)

2x Samsung 990 Pro with NvME PCIE Controller (Bifurcation enabled after BIoS update)

PBS Box will keep 7 day backups.

Backup at 21:00 everyday about 71 VM's.

Note - not a primary or BCDR box just a offsite backup.

Any advice, recommendations etc appreciated. Discussions and critique also welcomed re the "Special Device"

 

[d.oishi]

As I understand it, using a special device is not mandatory when running PBS on HDDs.
I also think your concern about what happens if the special device fails is valid.

Since this is for offsite backups, if performance is not a priority, I think an HDD-only configuration is also a reasonable option.

 

[woma]

ZFS is not about preventing failures. It is more about building things in a way that they can be easily reparied as soon something will break. If your concern is losing one disk use a mirror of two. If your scenario is losing two disks then use a mirror of three of them or anything else that means no data loss in that case.

Better term for device in ZFS context would be "vdev" or "virtual device", which are building blocks for ZFS pools.

Pools are made out of vdevs.
A vdev is made of physical disks/partitions/files or other vdevs.

The tricky part is that in simplest case a vdev is defined by giving a device name.
But you are not restricted to a single device name anywhere a vdev is defined.
You can choose whatever vdev definition you like that fits your redundancy needs and number of drives/partitions available.

Log, cache, special also take a vdev definition and instead of vdev "/dev/sda" you can choose other vdevs like "mirror /dev/sdb1 /dev/sdc1" or anything else.