Raid 5 with USB disks

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Raid 5 with USB disks

Postby ebelloli on Thu Jan 02, 2014 10:59 am

Hi all,
I installed on a Mink 16 a RAID 5 for backup purpose on my portable PC: it worked BUT gnome-disks reported the Raid to be "degraded" and to fix it it would took something like 20 hours.

I did the same on a different portable PC with Mint 14 and haven't got the problem.

Now switching the Raid from a PC to another everything works, but the one with Mint 16 continue to claim that the Raid is degraded, while on the Mint 14 it is reported as OK.

As it is a backub system I would like to be sure that everything is OK.

Below all the tech details, and the only visible (to me) difference is the version of gnome-disk-utility.

Thanks, evelino

PC Mint 16 - 64 bit
mdadm - v3.2.5 - 18th May 2012
gnome-disk-utility - Version: 3.8.2-1ubuntu2

PC Mint 14 - 32 bit
mdadm - v3.2.5 - 18th May 2012 (same on both PC)
gnome-disk-utility - Version: 3.6.1-0ubuntu1 (older...)

I used 2 different set of disks, some results:
[*]Set 1: 3 disks of 750GB each, different manifactures and models
[*]Set 2: 3 disks of 1TB each, same manifactures and models

Both set of disks are connected to a single USB port of the PC through a USB 3 hub
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Re: Raid 5 with USB disks

Postby grimdestripador on Fri Jan 03, 2014 6:05 pm

While I appreciate trying new things. RAID is not a backup nor was it intended to run over USB. I can go on and on about technical details concerning the futile nature of your efforts. May I suggest you purchase a NAS, having the RAID connect to SATA drives directly is the way to go. Also RAID is not backup, its goal is high availability (uptime during critial work hours), it does not prevent you/virus/linux from deleting/modifying files, and has no way to restore them back to their previous state. I understand in this case you may be using a laptop with USB harddrives, as a backup. But for the sake of your data, don't use RAID over USB.

You say that you use a USB hub, thus all data is going through only 1 connection. In raid, ifyou have 5 drives. and need to write 4 MB, in the end you end up writing 5 Megs. The main advantage of RAID (other than redundency) is that read speed will be faster, but since which is normally 5 parallel connections through SATA is now routed through a single serial USB. You are better off saving to a single USB drive directly.
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Re: Raid 5 with USB disks

Postby ebelloli on Thu Jan 09, 2014 11:36 am

Thanks @grimdestripador ,
I'm aware of the issues you speak of, however I've a few spare USB disks and wanted to use them for storing non-critical data.

Moreover I wanted to play with something new :)

Up to now I have a working mobile setup of 3 disks that seems (cross my fingers) to be quite stable.

ciao, evelino
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