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List:       linux1394-user
Subject:    Re: sbp2 external hdd problems : slow read/write speeds
From:       Stefan Richter <stefanr () s5r6 ! in-berlin ! de>
Date:       2004-08-28 14:43:46
Message-ID: AABCBD1E-F900-11D8-B8F5-00039303BE58 () s5r6 ! in-berlin ! de
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On Aug 28, Laurent Perez wrote:
> Yeah, I guess it's my problem. I've just tried large files transfers
> from the root ide drive to the firewire drives and speeds are correct.
> Only transfers between sbp2 drives are affected.

They have of course to share the overall bandwith. As long as there
is only a single host adapter, all connected nodes are joined to a
single FireWire bus and have to share the bus' bandwith. What is more,
when you copy from one SBP-2 device to another, there are no direct
transmissions between those devices. The host PC plays some kind of a
store-and-forward role.

(The source device sends data to PC through 1394 write transaction;
the PC makes all the conversions from DMA buffer content to source
filesystem read IO result, then converts from target filesystem
write request to DMA buffer content; and at last the target device
fetches the data by 1394 read transaction.)

Therefore, a copy operation from FireWire disk to FireWire disk is
roughly half as fast as between IDE disk and FireWire disk --- if
FireWire bus bandwidth were the dominating factor. In fact, I just
measured 65% performance of a FW-FW operation compared to a IDE-FW
operation. (All disks are 5400rpm disks, op was a large file copy
from and to reiserfs, source drives were the same model on FW and
IDE. In absolute numbers: I get 12 MByte/s versus 18 MByte/s. If I
tweak bus parameters for maximum bandwith of small buses, the
numbers are 75%, 16 MByte/s, 21 MByte/s.)

 > Lets wait for a reliable 1394 2.6+ driver ;-/

You could try the latest drivers from linux1394.org. The trunk
directory of the linux1394.org Subversion repository is a drop-in
replacement for linux-2.6/drivers/ieee1394/. (That does not mean
the latest drivers were reliable though.)
-- 
Stefan Richter
http://arcgraph.de/sr/



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