USB enclosure and partition size

[Keith Lofstrom]

> ... problems with USB enclosure hangs with Fedora Core 2 ...

A friend of mine is working on this problem.  It is real, and there
seems to be a kernel flaw causing it - something to do with host_reset. 
Contact me and I will forward his email address to you.

I have seen problems with large drives in some USB enclosures and
not others.  I first saw a permanent hang with *any* size drive
with late 2.4 kernels and external drives using the Cypress CY7C68013
USB2 chipset.  I did not see the problem with two other USB enclosures
that used different - and slower - chipsets.  

The 2.6 kernels do not have the old 2.4 problem (a permanent hang).
The new version of the problem is a big slowdown in transfer rate after
an initial burst on small ( <137 GB ) drives.  On large drives, the
slowdown is extreme - the data still moves, but there are 5 minute
(yes, 300 second!) pauses in the data transfer.  Again, this only
happens with the Cypress chipsets, and the problem does not appear
under Windoze. 

My guess is that it has something to do with the speed of the Cypress
chipset, and the size of the data chunks with LBA48 addressing.  Most
USB2 chipsets are single buffered;  there are gaps in the data transfer
allowing the kernel to do housekeeping.  The Cypress chipset is double
buffered, and fills one buffer while spewing another, allowing it to
go at full USB2 bandwidth during write.  

It will help to learn the chipset in your enclosure, which may appear
in /proc/bus/usb/devices .  You might also open the case and read the
chipset markings off the big LSI on the USB2 interface board.

I BCCed my friend, so perhaps he can weigh in here.   Please help the
young fellow achieve fame and fortune (or at least resume points) by
providing observations that will help him debug this pesky problem.

Keith

-- 
Keith Lofstrom           keithl at ieee.org         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs