From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Pittman Subject: USB disks for RAID storage (was Re: Please help me save my data) Date: Sun, 17 Sep 2006 09:48:04 +1000 Message-ID: <87odtfe5l7.fsf_-_@rimspace.net> References: <59430.213.136.43.252.1157976989.squirrel@webmail.adocca.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids "Patrick Hoover" writes: > Is anyone else having issues with USB interfaced disks to implement > RAID? Any thoughts on Pros / Cons for doing this? I have done, as a trial. USB disk support in recent 2.6 based distributions was quite stable and reliable, and I had no significant problems with RAID arrays -- including constructing arrays at boot time. However, USB disk performance was not great; I wouldn't want to run more than one, or possibly two, disks on a single USB controller. Anything more than that and you really see performance drop off. Also, the USB transaction latency seems a bit greater than IDE or SATA, so there are longer delays in data getting in or out of the system -- which add up, and make workloads with lots of fsync and small files painful. For bulk storage of large data with low performance requirements chaining a whole bunch of USB disks off a single controller would be acceptable, but otherwise I wouldn't bother. I didn't investigate IEEE-1394 connected disks, but I anticipate them to have similar issues with controller latency and bandwidth. Tests with two disks suggest a similar set of issues.[1] Regards, Daniel Footnotes: [1] Also, Linux optimizes the 1394 bus less well than it could, so performance is hurt by that a bit. -- Digital Infrastructure Solutions -- making IT simple, stable and secure Phone: 0401 155 707 email: contact@digital-infrastructure.com.au http://digital-infrastructure.com.au/