Re: Linux Software RAID on External Drives

> Does anyone have experience using Linux software raid (mdtools) to
>create disk arrays by linking multiple external drives together? Is it
>reliable? What are the preffered busses -- USB2, IEEE 1394, Fiber, etc?
>And above all, what do you think will be the most cost-effective (yet
>still viable) solution?

Hi Brice,

I'm running two linux software-raid raid5-arrays at home - one older array
using 4 internal drives (Started out with 60G IBM drives, but is now a mix
of 60G and 8G WD-drives), and one newer using 4 120G WD-drives in firewire
enclosures.

 From a servicing-pow, I can strongly recommend using external drives.
Having a drive fail on an internal channel means noting down which drive
fails, powering the box down and then extracting and replacing the /right/
drive, which can be a problem in cramped cases with long, single-unit ide
cables flowing everywhere. I'm sure using IDE hot-swap cages would have
simplified the problem somewhat, but I did not do this at the time.

The external firewire array is a much better solution. I have 2 3-port
FW-cards, and run a cable from a controller port to each drive. Managing the
disks was a bit of a bother in the beginning as the drivers would reorder
the drives when devices were attached and removed, but in the raid itself it
works well. I do not treat it as hot-swap, and power the system down for
maintainance. The downside with this array is performance. I have not been
able to gat any decent performance, probably both due to channel overhead
and PCI saturation. Still, as a network diskserver, I do not need more than
12MB/s read or write performance, as that is what the server can use on my
100mbps network.

For my next project, I'm going for an SATA raid. There are a number of
solutions that support running external SATA devices, and SATA enclosures
are priced the same or cheaper than FW enclosures (fewer active parts in the
enclosure).

I have not tried USB, except to see that it works, but I suspect that you
here too would be suited by using multiple controllers and not just multiple
ports to connect the drives to.

I hope this is useful for you. Feel free to mail me off-list if you have
questions.

Yours,
-S

-- 
Simen Thoresen, Wulfkit Support, Dolphin ICS
http://www.tysland.com/~simentt/cluster
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