Is it possible to implement RAID 1 with an external usb device? I would't see why not, but just want to be certain that their are no known issues before purchasing(an external usb hard drive enclosure).

I have read tldp.org's "software raid howto" and have assumed that I would just need to make the necessary /dev/[usbdevice] entry in the raid configuration file?

You can but you will have a lot of latency problems and problably instablity problems. Its better if you use firewire than using USB.

I am not sure that this statement is entirely true.

If two (2) USB drives were each attached to a seperate usb 2.0 root hub with no other devices connected, then "theoretically" you would get the full bandwidth to each device, and would be at the mercy of the latency and speed of the enclosure's USB <-> IDE bridge. (sorry for the runon)

I belive that bmgz is correct in assuming that it would work, but i would definitely caution on how the devices are connected to the computer.

Also, if you are looking for something that is fault tollerant, you might want to consider switching off USB / FIREWIRE completely (if possible). IDE raid cards are pretty cheap these days, and will do a much better job than the software raid that comes with linux.

Ok I am dead set on a pci raid controller+ 2 swappable drive enclosures!...

If you are just going to be doing mirroring, you can save yourself some $ if you buy a pci raid controller that does not do raid 5. There are pci raid controllers that JUST do Raid 0 and Raid 1. I have used the ones from promise ( http://www.promise.com/ ) under linux.

If you are looking to implement hot swap, make sure your card and enclosure BOTH support it. Just because its a RAID card does not mean it supports hot swap.

If you are going to use Highpoint, INTEL, Promise, Silicon Image, VIA IDE controller use Linux software RAID instead than one that comes with the controller. The software RAID from controllers is not any better than Linux software RAID. If the controller supports hot-swap, the module (driver) have to support it too which it does not. SCSI is the only one that support hot-swap for IDE (SCSI to IDE bridge) or SCSI devices in Linux. At this time Linux does not support how-swap for SATA.

USB has higher latency than Firewire, so forget using USB. There are Fireware enclosures that have RAID 0, RAID 1, and RAID 5 though it needs Firewire 800. I do not know if Firewire 800 is supported in Linux.

Software raid, who said anything about software raid. I was referring to a HARDWARE RAID controller card. There is no reason to buy a raid card that only provides software raid through the driver.

If you are planning to go w/ software raid, just buy another dual channel IDE controller and run linux raid as mentioned by Electro.

Anothter note on hot swap, If the user is only mirroring, the drivers for a hardware raid setup do not necessarily need to know about the hot swap. (ok, exception, you need to notify the user of the failure event) The controller should be able to handle everything w/o any interaction from the OS. Why get the OS involved at all when its just a simple mirroring setup. Unplug the drive, plug in the new one.

Also, please correct me if im wrong... but dont most linux drivers for raid controllers use the SCSI sub system anyways? I have yet to come across a raid card that doesnt yeild /dev/sda or similar as the block device to the array.

watch out... Promise controllers are software based & pieces of crap.

OK, maybe that's a bit of a generalization, but I can say for a fact that the newish Fasttrack S150 SX4 is software based and a piece of dung - hence its price being right around that of an IDE controller (because it is just an IDE controller).

Promise likes to use its own, proprietary algorithms for figuring the array, which means if something goes wrong, you're stuck with the promise card. You cannot simply unplug the drive from the card and plug it into the mobo, you're stuck with promise.

The Promise card also allows the machine to boot even when it fails. It runs in a critical state in which all writes corrupt the data when you recover from the critical state. Example: boot up in critical state, create a new directory or file at the root of the raid, and ALL your data is GONE! Promise support will tell you to go buy a 3rd party data recovery program.

edit to add: My Promise card would ONLY run under ONE kernel & could not be recompiled for another... meaning I am stuck with 2.4.20-8 (even the minor release & build number are specified) which has known security problems.... but I can do nothing about it.

Linux software RAIDs have the advantage of both drives ready to work when the RAID fails. If one drive fails, pull it off the RAID & plug it in to a normal IDE/SATA port, & you're all set.

If you're going to go hardware RAID - you get what you pay for. $150 is NOT going to get you hardware acceleration, it's going to get you a normal controller card with some proprietary BS array method.

3ware makes excellent RAID controllers.