[Novalug] best hard disk setup for home file server?

John Franklin franklin@elfie.org
Tue Oct 13 11:35:25 EDT 2009


On Oct 13, 2009, at 9:38 AM, Richard Ertel wrote:

> in light of the current problems i am having with my home file server,
> i want to reconsider my choice for how i configured hard disks in my
> server.
>
> as said before, i currently have two 1.5 TB drives and two 1.0 TB
> drives, all standard 3.5" internal disks.
>
> four 1.0 TB partitions are in RAID-5 configuration, and the remaining
> two 500 GB partitions are RAID-1. these two arrays are combined via
> LVM into one logical volume of 3.5 TB.

That's a bit of a weird RAID configuration. Two RAID-5 volumes lashed  
together would be RAID-50, similarly, two RAID-1 configurations would  
be RAID-10.  This would be....  RAID-150?  RAID-510?

> my current situation has the new brand new 1.5 TB drives dying, which
> of course kills all my data. they are identical drives (seagate), same
> model number, maybe same manufacturing batch. both dying at the same
> time.

This is a common problem.  Given a set of identical disks all bought  
at the same time, the MTBF will be reached about the same time.  Once  
one drive starts to fail, the odds of another failing during the  
rebuild -- a stressful operation for the drives -- is higher than  
normal.  AIUI, this is the failure case that inspired RAID-6, the two  
parity-drive variant of RAID5.  In RAID-6, when one drive dies you  
"degrade" to a RAID-5 volume.  Once it finishes the rebuild, you're  
back to the double protected RAID-6.

> does anyone have any experience RAIDing external USB drives in linux?
> should i expect reliability to increase if i move all 4 drives to 4
> external SATA to USB enclosures (5.25" enclosures with fans)? are
> these enclosures suitable for 24/7 operation? would read and write
> speed suffer (all transfers are over gigabit network)?

External USB will be painfully slow, and prone to other failures.  Too  
many external, exposed parts.  The file server I built here at home  
was first on an old Athlon 64 with a four-drive version of [1] .  It  
has a fan on the back to keep the drives cool, no external parts to  
trip over, and works with any SATA controller.

That worked fine, but when I decided to rebuild it as a storage and VM  
server, I bought a Dell 2900 mk III.  Dell had a special at the time  
that got me an 8-core system with the PERC/6 RAID controller for about  
$1200.  (Only one 80G drive, and a gig of RAM, had to upgrade those  
later.)  The 2900 has 8 drive bays, and supports hardware RAID-6.

[1] http://www.newegg.com/Product/Product.aspx?Item=N82E16816215048

> if all those USB drives running through a USB hub to a server is ok,
> then what about ditching my tower and running them all to a netbook as
> a server? i've seen that argument made once before, citing built-in
> ups (battery), built-in monitor, low power draw and other factors as
> big benefits to a netbook as server.

Netbooks are Intel Atom processors.  I would not expect an Atom to  
keep up with the demands of an MD RAID-5 array.  I'm not sure if USB  
would be the bigger bottleneck or the Atom.

> or am i worrying too much and what i have on my hands is just a fluke,
> and in the future i should mix drive manufacturers/models to avoid
> simultaneous failure?


I would stick with the same manufacturers and models as having the  
same models removes a lot of other issues.

If you're concerned about all of them coming from the same batch, buy  
them over time and/or from multiple vendors.   Personally, I think you  
would be better served by getting a couple extra drives to keep on a  
shelf for when drives fail and rebuild as a RAID-6 configuration.   
Alternately, consider setting up a ZFS volume, which has its own RAID- 
Z protection built-in.

jf
-- 
John Franklin
franklin@elfie.org
ICBM: 39º 01' 58.4"N 77º 24' 49.6"W Z+84m

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