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Comment by M95D | Hacker News Reader

USB is unreliable.

I used btrfs raid0 on USB drives for more than a year. Every month or so, a drive would disconnect from the bus and immediately redetected as another device (sde->sdf). Btrfs does not auto-recover from this. The choices are 1) reboot and scrub, which recovers the missing drive without doing a full resync, but it needs a reboot (any hosted site is offline for 3 minutes) and scrub takes a long time reading in the background, or 2) run btrfs replace which doesn't need a reboot, but the full resync takes even longer than a scrub and increases wear if it's a ssd because it wipes everything and writes all data again.

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I agree that USB is unreliable.

I will point out that if you use ZFS instead of btrfs, you can specify drives to be detected via their serial number names rather than their attachment points, so a reconnect will not require a reboot.

Still, don't depend on USB for anything meant to be permanently connected.

USB is unreliable but it's working for me. I've had zero disconnects in a couple of years of using a Terramaster USB-C DAS. I've heard of the problems enough I've even searched logs for it.

I've wondered if my experience is different because I'm using single disks (but still ZFS) instead of any RAID. There is rarely transfer happening across all of the disks.

Can't say. The power source for the drives is also important. I do use a USB 2.5" HDD without an external power source for one of the SBCs I have, and that's stable, but that SBC is powered directly from the GPIO pins, not USB.

Unfortunately, where I need it the most - the router which is also a NAS - can't use directly-powered USB HDDs. Not enough ports. I had to use a hub. I tried 4 models, two self-powered and two powered by router's USB, and none of them was stable. I also tried 3 models of USB-SATA adapters. Two self-powered, one powered by hub (connected to the hubs that had separate power - didn't work otherwise). None of them was stable. It was always the USB-SATA adapters/racks that disconnected, not the hubs.

Then I bought a mPCIe 4-port SATA controller, Marvell chip. Didn't work. It freeze randomly and woudn't even unfreeze with a router reboot. Possibly too much power draw. Then I put a 2-port SATA, ASM1062 and a port replicator. That one works. 2 years and not one disconnect. The cables are a complete mess.

I'm using RAID on my Terramaster DAS and it's been working fine for me. I think it's less "USB is unreliable" and more "Some SATA-USB adapters are unreliable".

The Terramaster one is pretty widely used in home setups and seems perfectly fine.

Be warned that Terramaster does RAID with 512B stripe size. If it fails, you can't mount the drives in Linux.

I have not had this issue myself. Drives connected for around 6 months in raid without issue. But also, you should mount your drives using partition UUID rather than whatever linux decides to name them which is not stable as you'd noticed.

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