[Server-devel] [XSCE] Re: Root fs on XO1

[James Cameron]

On Mon, Aug 12, 2013 at 11:44:58AM -0400, George Hunt wrote:
> I was really fortunate, in my testing yesterday.  I happened to have
> a USB ethernet dongle, and a 5v tplink 3020 wifi unit attached when
> I started testing.  The WD disk did not spin up.  I removed the
> ethernet and wifi loads, and it spun up correctly. The fortunate
> part was that a vulnerability was exposed, and the opportunity to
> address it is at hand.
> 
> I'm going to spend some time today to get numbers for the
> interfering loads.  The XO4 under test is connected to a "watts up"
> power meter. This morning, idle, the watts-up indicated 3.3w. I did
> an "ls" on the mounted drive, and saw a transient on the meter to
> something between 7 and 8 watts.  I'm sure I, and the meter, didn't
> see the whole event. But after a length of time (probably spin up)
> the power was 4.6 (maybe the additional cpu and spinning current).
> Letting the XO4, and the hard disk, go to idle, I removed the hard
> disk USB connector.  After a short time, the power decreased (after
>  a long time at idle) from 4.0w to 2.2w.

Was there a main battery in the laptop?  The embedded controller may
deliver some of that power to the main battery, and the rate of
delivery may change.  So I would normally remove the main battery
during power tests.

I agree that such a power meter won't see enough data about the event,
and the accuracy of the meter at such small values is often unreliable.

A current meter on the USB cable is probably more appropriate, but
avoid adding too much burden voltage or devices will declare the
voltage inadequate.

> I've noticed that just hitting the projecting HD USB connector can
> cause a disconnect/reconnect cycle displayed on an open console
> window.  Does this often crash an external disk? Does this
> observation favor ext3 or ext4 over ext2?

This sounds particularly bad.  I suggest looking for other drives, USB
cables, or try a different port.

You will experience corruption of the filesystem if a power glitch
occurs at the wrong time.  I've seen it happen twice in the past
month.  The corruption can be writes placed in the wrong location on
disk; the host asks for a write to block n, the data is later found at
block m.  Neither ext2, ext3, or ext4 can handle this.  fsck will
usually not detect it.

What SKU of XO-4 is this?

-- 
James Cameron
http://quozl.linux.org.au/