[LAU] drive bays and hardware RAID

[Arnold Krille]

Hi,

On Tuesday 04 May 2010 16:12:39 plutek wrote:
> i'm looking at my pile of external audio drives and backup drives, and
>  wondering about better solutions.
> a friend has recently mentioned multiple-drive bays, which allow you to
>  swap raw drives in/out at will, eliminating all the individual enclosures.
>  we also had a discussion about bays which implement hardware RAID for
>  realtime mirroring.
> i'm wondering if any of you have experience with these sorts of devices in
>  the context of linux multitrack audio work. specific concerns might be
>  things like:
> 1. reduction of total throughput in a combined-disk device relative to
>  separate drive enclosures connected to their own USB ports

I think the bottleneck here is usb, not disks...

> 2. reduction of total throughput caused by the RAID mirroring process, even
>  when it is done by dedicated hardware
> 3. linux compatibility
> 4. expense
> any experience and/or recommendations about doing this sort of thing would
>  be most welcome! thanks in advance.

Here is my advice:

Don't do hardware-raid! Neither the real nor the "soft" hardware raid help you 
that much. What do you do when the controller fails?

With a hardware-raid you have to have a second of the same kind in stock to 
get back the data on your disks. Don't even think about not having a spare 
controller and buying one when yours fails.
Murphies law says the controller will fail at exactly the time you have a 
_very_ important project going on and the controller to use is not sold 
anymore.

With a software-raid you just plug the disks in another machine/controller and 
return to working on your project.
The "reduced" throughput of a software-raid is worth the ease of use. And its 
not that "reduced" at all.

Oh, and use only raid1 or combinations of 0 and 1. For all the others see 
http://baarf.com.

And if you want more freedom for your disks and partitions, use lvm. Just this 
month I had a disk in an array of 5 that announced its failing in smart. 
Marked the raid1-copy of the systempartition on that disk as faulty (hot-spare 
kicked in), did lvmove to move all the logical volume off that disk and carried 
the disk to my dealer for an rma. Two weeks later I shoved in the 
replacement... Server uptime: not interrupted. Admins sanity: not influenced.
Of course that only works if you have *some* free space on the physical 
volumes.

Arnold
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