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

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

On Tuesday 09 February 2010 16:11:14 Stroller wrote:
> On 9 Feb 2010, at 13:57, J. Roeleveld wrote:
> > ...
> > 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.
> 
> Exactly. Except the partitions extend, in the same positions, across
> all the disks.
> 
> You cannot remove one disk from the array and repartition it, because
> the partition is across the array, not the disk. The single disk,
> removed from a RAID 5 (specified by Paul Hartman) array does not
> contain any partitions, just one stripe of them.
> 
> I apologise if I'm misunderstanding something here, or if your RAID
> works differently to mine.
> 
> Stroller.
> 

Stroller, it is my understanding that you use hardware raid adapters?
If that is the case, then the mentioned method won't work for you and if your 
raid-adapters already align everything properly, then you shouldn't notice any 
problems with these drives.
It would, however, be interesting to know how hardware raid adapters handle 
these 4KB sector-sizes.

I believe Paul Hartman is, like me, using Linux Sofware raid (mdadm+kernel 
drivers).

In that case, you can do either of the following:
Put the whole disk into the RAID, eg:
mdadm --create --level=5 --devices=6 /dev/sd[abcdef]
Or, you create 1 or more partitions on the disk and use these, eg:
mdadm --create --level=5 --devices=6 /dev/sd[abcdef]1

To have linux auto-detect for raid devices work, as far as I know, the 
partitioning method is required.
For that, I created a single full-disk partition on my drives:
--
# fdisk -l -u /dev/sda

Disk /dev/sda: 1500.3 GB, 1500301910016 bytes
255 heads, 63 sectors/track, 182401 cylinders, total 2930277168 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0xda7d8d6d

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1              64  2930277167  1465138552   fd  Linux raid autodetect
--

I, after reading this, redid the array with the partition starting at sector 
64. Paul was unfortunate to have already filled his disks before this thread 
appeared.

The downside is: you loose one sector, but the advantage is a much improved 
performance (Or more precisely, not incur the performance penalty from having 
misaligned partitions)

--
Joost Roeleveld