On 23/01/18 21:16, Linus Lüssing wrote: > Hi, > > By chance I found this statement in the Linux RAID Wiki: > > "Do NOT use [USB devices] as part of your array. They have > a timeout/disconnect mechanism which interacts very > badly with the raid code." [0] > > Could someone elaborate further on this? Does "interacts very > badly" mean that there will be potential data loss / data > corruption? Or does "very badly" just mean short, temporary > performance issues / lags upon a disk failure? I would expect that the majority of USB disk issues can be avoided by due care and attention. USB buses are rarely reset or re-initialised without provocation. The cause is generally flaky hardware on the bus, plugging or unplugging devices, devices that sleep waking up, sudden changes in power requirements of devices, and other physical events. When using USB disks, I'd give the following advice: 1. Connect directly to a USB port on the computer, not via a hub. That way you don't have other devices on the same bus that could cause trouble. 2. Avoid plugging other hardware in and out of the other USB buses, and certainly avoid it on the bus with the disk. Keep the bus physically stable. 3. Avoid having high power devices on USB, like DVD burners. If the disk has an optional external power supply, use it. 4. Ensure your USB disks are cooled appropriately. Some USB disk enclosures are very tight around the disk and can overheat. Freestanding USB-to-SATA converters where you plug the bare disk in directly can be good (but beware of dust if you are leaving them for a while). 5. Use good cables and avoid plugging and unplugging things too much, to limit the risk of broken wires and worn contacts. 6. Don't rely on the USB drive - use it as an extra. They are great for taking extra backups, and to provide additional redundancy during risky operations (such as to add an asymmetric second parity drive to a raid5 set before replacing the raid5 disks with bigger devices). 7. Don't use "memory stick" USB drives for raid - these have very limited write lifetimes and are easily corrupted. 8. And for the love of $DEITY, /don't/ have USB drives connected by cables where you will trip over them and throw the drive across the room. (As Yoda says, good judgement comes from experience. Experience comes from bad judgement!) > > Regards, Linus > > [0]: https://raid.wiki.kernel.org/index.php/Choosing_your_hardware,_and_what_is_a_device%3F#USB_devices -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
