Re: [gentoo-user] 1-Terabyte drives - 4K sector sizes? -> bar performance so far

["J. Roeleveld" <joost@antarean.org>]

On Tuesday 09 February 2010 13:46:40 Stroller wrote:
> On 9 Feb 2010, at 00:27, Neil Bothwick wrote:
> > On Mon, 8 Feb 2010 14:34:01 -0600, Paul Hartman wrote:
> >> Thanks for the info everyone, but do you understand the agony I am
> >> now
> >> suffering at the fact that all disk in my system (including all parts
> >> of my RAID5) are starting on sector 63 and I don't have sufficient
> >> free space (or free time) to repartition them? :)
> >
> > With the RAID, you could fail one disk, repartition, re-add it,
> > rinse and
> > repeat. But that doesn't take care of the time issue.
> 
> Aren't you thinking of LVM, or something?
> 
> Stroller.
> 

Not sure where LVM would fit into this, as then you'd need to offload the data 
from that PV (Physical Volume) to a different PV first.

With Raid (NOT striping) you can remove one disk, leaving the Raid-array in a 
reduced state. Then repartition the disk you removed, repartition and then re-
add the disk to the array.
Wait for the rebuild to complete and do the same with the next disk in the 
array.
Eg: (for a 3-disk raid5):
1) remove disk-1 from raid
2) repartition disk-1
3) add disk-1 as new disk to raid
4) wait for the synchronisation to finish
5) remove disk-2 from raid
6) repartition disk-2
7) add disk-2 as new disk to raid
8) wait for the synchronisation to finish
9) remove disk-3 from raid
10) repartition disk-3
11) add disk-3 as new disk to raid
12) wait for the synchronisation to finish

(These steps can easily be adapted for any size and type of raid, apart from 
striping/raid-0)

I do, however, see a potential problem, if you repartition starting from 
sector 64 instead of from sector 63, the disk has 1 sector less, which means 
4KB less in size.
The Raid-array may not accept the re-partitioned disk back into the array 
because it's not big enough for the array.

I had this issue with an older system once where I replaced a dead 80GB (Yes, 
I did say "old" :) ) with a new 80GB drive. This drive was actually a few KB 
smaller in size and the RAID would refuse to accept it.

--
Joost Roeleveld