RE: Spares and partitioning huge disks

This is from "man mdadm":
As  well  as  reporting  events,  mdadm may move a spare drive from one
array to another if they are in the same spare-group and if the  desti-
nation array has a failed drive but not spares.

You can do what you want.  I have never tried.  My arrays are too different.
I don't want to waste an 18Gig spare on a 256M array.

Guy

-----Original Message-----
From: linux-raid-owner@vger.kernel.org
[mailto:linux-raid-owner@vger.kernel.org] On Behalf Of maarten
Sent: Thursday, January 06, 2005 9:17 AM
To: linux-raid@vger.kernel.org
Subject: Spares and partitioning huge disks


Hi

I just got my 4 new 250GB disks.  I have read someone on this list
advocating 
that it is better to build arrays with smaller volumes, as that decreases
the 
chance of failure, especially failures of two disks in a raid5
configuration. 

The idea behind it was that since a drive gets kicked when a read-error 
occurs, the chance is lower that a 40 GB part develops a read error than for

the full size 250 GB.  Thus, if you have 24 40GB parts, there is no fatal
two 
disk failure when part sda6 and part sdc4 develop a bad sector at the same 
time. On the other hand, if the (full-size) disk sda1 and sdc1 do fail at
the 
same time, you're in deep shit. 
I thought it was real insightful, so I would like to try that now.

(Thanks to the original poster, I don't recall your name, sorry)

Now my two questions regarding this.

1) What is better, make 6 raid5 arrays consisting of all 40GB partitions and

group them in a LVM set, or group them in a raid-0 set (if the latter is
even 
possible that is) ?

2) Seen as the 'physical' volumes are now 40 GB, I could add an older 80GB 
disk partitioned in two 40GB halves, and use those two as hot-spares. 
However, for that to work you'd have to be able to add the spares to _all_ 
raid sets, not specific ones, if you understand what I mean.  So they would 
act as 'roaming' spares, and they would get used by the first array that 
needs a spare (when a failure occurs of course).  But... is this possible ? 

Thanks for any insights!
Maarten

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