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I've been running Ubuntu Server on a mini computer (fit-PC slim) for a few years. This box takes a single 2.5" IDE disk and has USB ports. I'm currently at Ubuntu Server 10.04. I use it mainly as a media server.

I experimented a while ago with mounting a 3.5" disk using a USB enclosure. It worked OK. My mode of use was to switch the disk on and off when I needed it, auto-mounting it when it was switched on.

I would now like to get an external USB disk (probably 500GB or 1TB) to expand storage. I'd like to be able to have the disk powered on all the time, but using as little power as possible when it is not in use. The fit-PC is a nice low-power consumption device and I'd like to keep things as low-power as I can.

I would be interested in advice on whether any particular disks are more suitable than others for this application. For example, are some brands better than others at spinning down and up under Linux in general / Ubuntu Server in particular? Any other experience with this kind of setup would be welcome.

I have the impression that standby/spindown of external disks can be hit and miss in Linux. So I was hoping for some views on that.

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up vote 1 down vote accepted

Generally speaking, any external USB hard disk will do. However, I think you should take the following into account:

  1. 2.5" disks are much more power-efficient than 3.5". They cost more, but you'll be able to connect using only one USB connector, no power bricks or second USB connector for power.

  2. Some Western Digital models have "smart" firmware that include "virtual" cdrom with backup software, etc. Avoid these, the software won't work in Linux and it just adds unnecessary complication. A honest simple USB-to-SATA adapter is preferred.

  3. I personally prefer buying a hard disk and an external enclosure separately, it is a bit more expensive but I know which disk model I'm getting, and I'm able to upgrade the disk in the future if needed (enclosure can be disassembled easily). Also, these separately-sold enclosures are usually very basic and don't include the features I don't need (backup buttons etc.)

Spin-down of an external hard drive

A hard drive can spin-down (enter a low-power mode) either automatically or manually. Some hard drives (e.g. so-called "green" ones) are shipped with Advanced Power Management feature enabled, and will spin down if inactive, most have this feature disabled by default.

You can use hdparm on Linux to control hard drive's power management features and put it into low-power mode manually if needed. hdparm man page says:

Many newer (2008 and later) USB drive enclosures now also support "SAT" (SCSI-ATA Command Translation) and therefore may also work with hdparm. Eg. recent WD "Passport" models and recent NexStar-3 enclosures.

  • You can do something like hdparm -S 240 /dev/sdX to enable automatic spin-down after 20 minutes of inactivity. Please see hdparm man page for info on S parameter values.

  • You can do hdparm -y /dev/sdX to put your drive to sleep immediately.

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+1 Thanks. I was hoping for some more on standby/spindown for always on USB disks. So I'll hold off on accept for now. – sudocode Dec 7 '11 at 10:18
@sudocode: I added a section on spin-down – haimg Dec 7 '11 at 19:08
As far as I understand, you can't use hdparm on a USB connected disk. Instead there are things like scsi-idle scripts. – sudocode Dec 8 '11 at 8:37

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