Re: [linux-usb-devel] 2.6.0-test1: random errors for USB disk

[David Brownell <david-b@pacbell.net>]

Alan Stern wrote:

> The information in your system logs is very clear.  Your USB drive worked 
> just great until it received a big data transfer.
> 
> Under 2.4, the largest WRITE transfer was 130048 bytes and it worked fine.  
> Under 2.6, the largest attempted WRITE transfer was 524288 bytes and it
> crashed the drive.  The two commands were otherwise identical.

Just to clarify:  there's another difference, and that's that 2.4 does
doing that smaller write one page at a time (write, wait, write, wait,...)
while 2.6 does it all at once (write, write, write, write, ... wait).

That difference is how I've seen usb-storage top 30 MByte/sec on USB
with 2.6 kernels, when 2.4 may not reach 10 MB/sec on the same hardware.

- Dave


> Presumably differences in the block I/O systems account for the difference
> in buffer sizes.  But I don't know of any way to tell Linux that the drive
> is unable to accept data transfers larger than some fixed limit.
> 
> Can anyone else suggest a way to solve this?
> 
> Alan Stern
> 
>