On Sat, Nov 03, 2012 at 09:14:08PM +0100, Miguel Dardenne wrote: > On 2012-11-03 17:50, Alan Stern wrote: > >> I get a USB disconnect of my external USB HDD about once per day. > >> Enabling USB debug in the kernel shows the first error as 'ehci_hcd > >> detected XactErr'. It happens only when the drive is idle. For > >> example, > >> I had a process writing on the HDD every 3 seconds and the problem > >> did > >> not occur for several weeks. > > > > Correction: These errors do not occur when the drive is idle. You > > can > > see in the log you attached: > > OK thanks for this. I then reformulate my statement: using the drive on > a frequent basis (3s period) prevents the problem from occuring. Then the problem might be related to the power management in the drive itself, not in the host OS. 2.5" drives tend to have a short spindown timeout, and the first operation performed after such timeout causes the drive to spin up. The spinup process consumes a lot of power (more than during sustained operation), and current fluctuations during this process might cause problems if any components in the power supply chain are marginal (even a lousy cable with too thin conductors can be problematic). You might be able to change APM settings of the hard drive using utilities like hdparm; however, this might not work with your particular WD external drive for several reasons: - Not all USB-SATA bridges can pass low-level ATA commands needed to change APM settings. If you purchase an USB-SATA enclosure and HDD separately, you could work around this problem by attaching the drive to a SATA port directly to perform this configuration (APM settings are usually persistent), but doing this with an external USB drive sold as a single item will probably void the warranty. Even worse, some external drives made by WD have the USB port actually soldered to the drive PCB itself, and the SATA interface is not accessible directly. - WD drives often need undocumented vendor-specific commands to control spindown (google for "wdidle" used for 3.5" WD Green drives; not sure about their 2.5" drives). Even if the appropriate tools exist, they might not work with USB-attached drives. Did you try to use another drive with this system? Using a drive with a separate power supply might at least rule out the power-related problems. You can also try to attach the drive to a powered USB 2.0 hub instead of directly attaching to the onboard port.
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